Title: Cybexsoft SMTP
Author: CybexSoft
Published: September 15, 2026
Last modified: September 15, 2026
---
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# Cybexsoft SMTP
By [CybexSoft](https://profiles.wordpress.org/rahul1099/)
[Download](https://downloads.wordpress.org/plugin/cybexsoft-smtp.1.0.1.zip)
* [Details](https://wordpress.org/plugins/cybexsoft-smtp/#description)
* [Reviews](https://wordpress.org/plugins/cybexsoft-smtp/#reviews)
* [Installation](https://wordpress.org/plugins/cybexsoft-smtp/#installation)
* [Development](https://wordpress.org/plugins/cybexsoft-smtp/#developers)
[Support](https://wordpress.org/support/plugin/cybexsoft-smtp/)
## Description
WordPress sends mail with PHP’s `mail()` function by default, which many hosts throttle
or block outright — so the message never arrives and nothing on the site says so.
This plugin replaces that transport and then keeps working after the swap, which
is the part most setups leave out:
* **Several mailers at once, with roles.** Add as many as you like and say which
one sends. Pro adds a backup that takes over automatically when the primary starts
refusing mail.
* **Nothing is silently lost.** A send that fails is held and retried on a widening
schedule instead of disappearing, and sending pauses while a mailer is plainly
broken rather than throwing every message at it.
* **A connection trace, step by step.** Watch the handshake with your mail server
or API key and see exactly which step fails, instead of reading “could not send”.
* **Deliverability diagnostics that tell you what to publish.** SPF, DKIM and DMARC
checked against your sending domain, with the record found, what it means, and
the exact change to make.
**Free features**
* Mailers: generic SMTP, Amazon SES (via SMTP), SendGrid, Mailgun, Brevo, SMTP2GO,
or default PHP mail — set up as many as you like and choose which one sends
* Email log with search, status filter, and CSV export — kept indefinitely
* Held mail: a message whose send fails is kept and retried on a widening schedule
instead of being lost
* Domain diagnostics: SPF, DKIM and DMARC record checks
* Send test emails and trace the connection to your mailer step by step, with a
rolling debug log for failures
* Force-from controls so other plugins can’t silently change your From address
* Allow & block lists: never email a blocked address or domain again
* Failure alerts: an email to you once sending starts failing, at a threshold you
set
* Credentials encrypted at rest, or supplied from wp-config.php and kept out of
the database entirely
**Cybexsoft SMTP Pro** is a companion plugin you install alongside this one. It
adds its features to the same settings screen, so there is still only one place
to configure anything. It is free during early access: ask us and we will email
you the download and a license key. It adds:
* Open & click tracking
* Automatic blocking of addresses that keep bouncing, and an allow-list-only mode
that stops a staging site emailing real customers
* Backup mailer with automatic failover
* Richer failure alerts: several recipients, your own counting window and quiet
period, and no alarm for a message the backup mailer already rescued
* Postmark, Resend, MailerSend, Mailjet, Elastic Email and Zoho ZeptoMail mailers,
plus Gmail & Outlook over OAuth
* Automatic log pruning on a retention window you set, plus a full content archive
* Weekly deliverability reports
### External services
This plugin can connect to the external services listed below. Sending email
necessarily
involves handing your message to a mail provider, so the mailer you choose is the
main one — but the plugin only ever talks to the provider you configured, using
credentials you supplied. Everything else here is optional and off until you act.
#### The mailer you configure
The plugin sends your outgoing WordPress email through whichever mailer you
select
under Settings. Five of the free mailers are third-party services of their own:
four HTTP APIs and Amazon SES. In each case what is sent is the outgoing message—
recipients, subject, body, attachments and headers — together with the credential
you configured, and only while that mailer is the selected one:
* **SendGrid** — sent to `https://api.sendgrid.com`. Service provided by
Twilio
SendGrid: [terms of service](https://www.twilio.com/en-us/legal/tos), [privacy policy](https://www.twilio.com/en-us/legal/privacy).
* **Mailgun** — sent to your configured Mailgun API host. Service provided by
Mailgun: [terms of service](https://www.mailgun.com/terms/), [privacy policy](https://www.mailgun.com/privacy-policy/).
* **Brevo** — sent to `https://api.brevo.com`. Service provided by Brevo:
[terms of service](https://www.brevo.com/legal/termsofuse/),
[privacy policy](https://www.brevo.com/legal/privacypolicy/).
* **SMTP2GO** — sent to `https://api.smtp2go.com`. Service provided by
SMTP2GO:
[terms of service](https://www.smtp2go.com/terms/), [privacy policy](https://www.smtp2go.com/privacy/).
* **Amazon SES** — sent over SMTP to `email-smtp..amazonaws.com`, for
the AWS region you select in the settings. What is sent is the outgoing message,
authenticated with the SES SMTP username and password you configured, and only
while Amazon SES is the selected mailer. Service provided by Amazon Web Services:
[service terms](https://aws.amazon.com/service-terms/), [privacy notice](https://aws.amazon.com/privacy/).
The remaining free mailers — generic SMTP and PHP mail — connect to the mail
server
you name in the settings, not to a service of ours. The Tools tab’s connection trace
opens a connection to that same server and stops before any message is sent.
For SendGrid and Mailgun, that same connection trace instead checks your key
against
the provider without sending any message: it requests https://api.sendgrid.com/v3/
scopes with your API key, or https://api.mailgun.net (or `api.eu.mailgun.net` on
the EU region) with your API key and the sending domain you configured. It runs
only when you click it, and nothing else about your site is sent.
#### Cybexsoft licence server
Used only once you have entered a Pro licence key under Cybexsoft SMTP License.
Your licence key, your site’s home URL, and the product and version being
licensed
are sent to `https://cybexsoft.com/api/licenses/verify` when a key is activated
and periodically thereafter to confirm it is still valid, and to https://cybexsoft.
com/api/licenses/deactivate when a key is removed. Nothing is sent while no licence
key is stored, and the free plugin never contacts these addresses at all — they
are used only by the Pro add-on.
Service provided by Cybexsoft: [terms of service](https://cybexsoft.com/terms-of-service),
[privacy policy](https://cybexsoft.com/privacy-policy).
#### “Get Pro for Free” request form
Used only if you open that form and submit it.
The name, email address, website and message you type, are emailed to
admin@cybexsoft.
com so we can send you the Pro download and a licence key. The request is sent through
this plugin’s own mailer — it is an ordinary email, not a background call — and
if your site cannot send mail yet, the form offers to open the same request in your
own email application instead.
#### Deactivation feedback
Used only if you choose a reason in the dialog shown when you deactivate the
plugin.
The dialog can be skipped, and skipping it sends nothing; deactivation proceeds
either way.
If you do submit a reason, your site’s URL, the plugin version and build, the
mailer
you had configured, the reason you picked and any note you wrote are emailed to
admin@cybexsoft.com.
#### showdns.net
The Deliverability tab links out to `https://showdns.net`, which runs the same
SPF, DKIM and DMARC checks from outside your server. The plugin makes no request
to it — nothing is sent unless you click the link, at which point your browser visits
it like any other site and the domain being checked appears in the URL.
Service provided by Cybexsoft: [privacy policy](https://showdns.net/privacy).
## Screenshots
[⌊The dashboard: which mailer is connected, SPF/DKIM/DMARC at a glance, a deliverability
score, 30-day sent, delivered, failed and open-rate figures, a 14-day volume chart,
a setup checklist, and the most recent messages with their opens and clicks.⌉⌊The
dashboard: which mailer is connected, SPF/DKIM/DMARC at a glance, a deliverability
score, 30-day sent, delivered, failed and open-rate figures, a 14-day volume chart,
a setup checklist, and the most recent messages with their opens and clicks.⌉[
The dashboard: which mailer is connected, SPF/DKIM/DMARC at a glance, a deliverability
score, 30-day sent, delivered, failed and open-rate figures, a 14-day volume chart,
a setup checklist, and the most recent messages with their opens and clicks.
[⌊The email log: every message with subject, recipient, status, date and engagement,
searchable and filterable by delivered or failed, with CSV export and a list of
the links your readers clicked most.⌉⌊The email log: every message with subject,
recipient, status, date and engagement, searchable and filterable by delivered or
failed, with CSV export and a list of the links your readers clicked most.⌉[
The email log: every message with subject, recipient, status, date and engagement,
searchable and filterable by delivered or failed, with CSV export and a list of
the links your readers clicked most.
[⌊Deliverability: SPF, DKIM and DMARC checked against your sending domain with the
records found, the exact DNS changes to make, infrastructure checks for the server
itself, and blocklist monitoring of your sending IP.⌉⌊Deliverability: SPF, DKIM
and DMARC checked against your sending domain with the records found, the exact
DNS changes to make, infrastructure checks for the server itself, and blocklist
monitoring of your sending IP.⌉[
Deliverability: SPF, DKIM and DMARC checked against your sending domain with the
records found, the exact DNS changes to make, infrastructure checks for the server
itself, and blocklist monitoring of your sending IP.
[⌊Settings: the mailers this site sends through and the role each one holds, a catalogue
of providers to add, and what should happen when the primary mailer starts refusing
mail.⌉⌊Settings: the mailers this site sends through and the role each one holds,
a catalogue of providers to add, and what should happen when the primary mailer
starts refusing mail.⌉[
Settings: the mailers this site sends through and the role each one holds, a catalogue
of providers to add, and what should happen when the primary mailer starts refusing
mail.
[[
## Installation
1. Upload the `cybexsoft-smtp` folder to `/wp-content/plugins/`, or install the zip
via Plugins Add New Upload Plugin.
2. Activate the plugin.
3. Go to Cybexsoft SMTP Settings and choose a mailer.
4. Send a test email from the Tools tab to confirm everything works.
## FAQ
### Which PHP versions are supported?
PHP 7.4 through the latest stable release.
### Does this store my SMTP password in plain text?
Not on any normal host. Passwords, API keys and OAuth tokens are encrypted before
they are written to the database (XSalsa20-Poly1305 via PHP’s sodium extension),
so a leaked database backup or an SQL injection in some other plugin does not expose
working mail credentials. The key is derived from your site’s WordPress salts; if
you rotate your salts on a schedule, define `CYBEX_SMTP_ENCRYPTION_KEY` in wp-config.
php first so stored credentials survive the rotation.
Sodium has been compiled into PHP by default since 7.2, so it is present on every
version this plugin supports. The one exception is a host that has deliberately
built PHP without it — there is then nothing to encrypt with, and credentials are
stored as you typed them. If that matters to you, ask your host whether `sodium`
is enabled, or look for it in a phpinfo report.
Either way, you can keep a credential out of the database entirely by defining it
in wp-config.php — `CYBEX_SMTP_PASSWORD`, `CYBEX_SMTP_SES_PASSWORD`, `CYBEX_SMTP_SENDGRID_API_KEY`,`
CYBEX_SMTP_MAILGUN_API_KEY`, `CYBEX_SMTP_BREVO_API_KEY` or `CYBEX_SMTP_SMTP2GO_API_KEY`.
A defined constant overrides whatever is stored, and is never written back to the
database.
If sodium is missing and a credential is stored anyway, the plugin now says so in
the admin rather than leaving you to find out from this page.
### How do I get Pro features?
Click **Get Pro for Free** in the plugin header (or next to Settings on the Plugins
screen), fill in the short form, and we will email you the Pro download along with
your license key.
The download is a separate plugin, **Cybexsoft SMTP Pro**, which you install alongside
this one: Plugins Add New Upload Plugin, then activate. Keep Cybexsoft SMTP active—
Pro extends it and will say so if it is missing. Your settings and email log stay
exactly where they are, and everything Pro adds appears on the same settings screen,
so there is still only one place to configure anything.
### Will updating Cybexsoft SMTP remove my Pro features?
No. They are two separate plugins, so an update to this one cannot touch the other.
Update either from the Plugins screen whenever you like.
It used to be a real risk, and this is why the two were separated. Pro was once
shipped as this same plugin with the extra code included, which meant an update
from WordPress.org replaced the whole directory and took the Pro code with it —
leaving the license behind and the features gone. Nothing to watch out for now.
### Where do I enter my Pro license key?
The **License** tab in Cybexsoft SMTP. Paste the key we emailed you there.
With the Pro plugin not yet installed the key is saved but shown as unverified,
because nothing on this side can check one — activating Cybexsoft SMTP Pro verifies
it.
### The request form says it could not send. Now what?
The form sends its request through the very mailer this plugin configures, so a
site that has not finished setting one up cannot email us either. When that happens
the form offers a link that opens the same request in your own email app instead—
nothing is lost.
### My email log shows a “Blocked” row. What is that?
A message that was deliberately not sent, rather than one that failed. It appears
when your block list stops a message before it reaches your mailer — the row records
who it was for and which rule matched. Blocked rows are counted separately from
failures and left out of your delivery rate, because nothing was ever handed to
a mail server.
### Does the email log slow my site down?
One small row is written per message, on the request that sends it. The log is indexed
on the columns the screens filter by, and Pro adds a retention window that prunes
old rows nightly if you would rather not keep them forever.
## Reviews
There are no reviews for this plugin.
## Contributors & Developers
“Cybexsoft SMTP” is open source software. The following people have contributed
to this plugin.
Contributors
* [ CybexSoft ](https://profiles.wordpress.org/rahul1099/)
[Translate “Cybexsoft SMTP” into your language.](https://translate.wordpress.org/projects/wp-plugins/cybexsoft-smtp)
### Interested in development?
[Browse the code](https://plugins.trac.wordpress.org/browser/cybexsoft-smtp/), check
out the [SVN repository](https://plugins.svn.wordpress.org/cybexsoft-smtp/), or
subscribe to the [development log](https://plugins.trac.wordpress.org/log/cybexsoft-smtp/)
by [RSS](https://plugins.trac.wordpress.org/log/cybexsoft-smtp/?limit=100&mode=stop_on_copy&format=rss).
## Changelog
#### 1.0.1
* Fix: the Plugins screen stopped with a fatal error (undefined constant KEEP_DATA_OPTION)
when loading the deactivation dialog.
#### 1.0.0
* Initial release.
* Connect a mailer: SMTP, Amazon SES, SendGrid, Mailgun, Brevo or SMTP2GO, with
Postmark, Gmail, Outlook / Microsoft 365, Resend, MailerSend, Mailjet, Elastic
Email and Zoho ZeptoMail in Pro. Add as many as you like and choose which one
sends.
* Email log: every message with its subject, recipient, status and date, searchable,
filterable and exportable to CSV.
* Held mail: a message whose send fails is kept and retried on a widening schedule
instead of being lost, and sending pauses while a mailer is plainly broken rather
than throwing every message at it.
* Failure alerts by email, at a threshold you set.
* Deliverability tab: SPF, DKIM and DMARC checks with the record that was found,
what it means, and what to publish.
* Access lists: stop mail to an address or domain before it reaches your mailer.
* Credentials are encrypted at rest, or can be supplied from wp-config.php constants
and kept out of the database entirely.
* Personal-data exporter and eraser for the email log, the mail queue and the debug
log.
* Pro: a backup mailer that takes over a message the primary refused, and can be
promoted to primary when the primary stops working; open and click tracking;
archived message content with re-send; weekly reports; bounce handling; blocklist
monitoring.
## Meta
* Version **1.0.1**
* Last updated **11 hours ago**
* Active installations **Fewer than 10**
* WordPress version ** 5.5 or higher **
* Tested up to **7.1**
* PHP version ** 7.4 or higher **
* Tags
* [deliverability](https://wordpress.org/plugins/tags/deliverability/)[email](https://wordpress.org/plugins/tags/email/)
[email log](https://wordpress.org/plugins/tags/email-log/)[mailer](https://wordpress.org/plugins/tags/mailer/)
[smtp](https://wordpress.org/plugins/tags/smtp/)
* [Advanced View](https://wordpress.org/plugins/cybexsoft-smtp/advanced/)
## Ratings
No reviews have been submitted yet.
[Your review](https://wordpress.org/support/plugin/cybexsoft-smtp/reviews/#new-post)
[See all reviews](https://wordpress.org/support/plugin/cybexsoft-smtp/reviews/)
## Contributors
* [ CybexSoft ](https://profiles.wordpress.org/rahul1099/)
## Support
Got something to say? Need help?
[View support forum](https://wordpress.org/support/plugin/cybexsoft-smtp/)