E-mails occasionally failing

jtg
(@favdes)

1 week, 4 days ago

Hello,

I was wondering if someone might be able to help us with this one.

We use the gift card plugin on our WordPress site. Also on there is the ‘Post SMTP’ plugin which sends e-mails from the site via the postmarkapp.com system.

Occasionally when a gift voucher is purchased the e-mail to the customer fails and we receive this error:

Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}

It appears that the gift card plugin is saying that an attachment is being added to the e-mail to the customer but it is zero sized.

Is this a known issue? Is there anything that we can do to prevent it?

Many thanks

Viewing 2 replies - 1 through 2 (of 2 total)

Plugin Author Codemenschen
(@codemenschen)

1 week, 4 days ago
Hello,

Thank you for your message.

Based on the error returned by the mail service:

Code: 422
Message: Unprocessable Entity
Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}

we can confirm that the email was rejected because an attachment in the outgoing message had a file size of 0 bytes.

At this stage, we cannot yet confirm which part of the process is generating or passing that empty attachment. To determine the exact cause, we would need some additional debugging on the site.

Could you please enable WordPress debugging and reproduce the issue if possible? The most useful next step would be to capture any PHP warnings/errors and mail-related logs at the time the voucher email fails.

If available, it would also help to check:
- the plugin/mail logs around the failed send attempt
- whether a PDF file was generated for that order
- the size of the generated file, if one exists
Once we have the debug output, we can review it further and identify where the empty attachment is coming from.

Kind regards,
Thread Starter jtg
(@favdes)

1 week ago

Hello,

Thank you for coming back to me. Here is an extra from the error log when the order was made:

[05-Jun-2026 01:55:27 UTC] PHP Warning: Undefined property: stdClass::$plugin in /home/ripleysgcco/public_html/wp-admin/includes/class-wp-automatic-updater.php on line 228
[05-Jun-2026 12:22:23 UTC] PHP Warning: file_get_contents(/home/ripleysgcco/public_html/wp-content/uploads/voucherpdfuploads/17806620119846836680335648-receipt.pdf): Failed to open stream: No such file or directory in /home/ripleysgcco/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanPostmarkMailEngine.php on line 55
[05-Jun-2026 12:22:24 UTC] ERROR PostmanWpMail: Exception code=0 message=Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}
[05-Jun-2026 12:22:44 UTC] PHP Warning: file_get_contents(/home/ripleysgcco/public_html/wp-content/uploads/voucherpdfuploads/17806620119846836680335648-receipt.pdf): Failed to open stream: No such file or directory in /home/ripleysgcco/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanPostmarkMailEngine.php on line 55
[05-Jun-2026 12:22:44 UTC] ERROR PostmanWpMail: Exception code=0 message=Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}
[05-Jun-2026 12:22:54 UTC] PHP Warning: file_get_contents(/home/ripleysgcco/public_html/wp-content/uploads/voucherpdfuploads/17806620119846836680335648-receipt.pdf): Failed to open stream: No such file or directory in /home/ripleysgcco/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanPostmarkMailEngine.php on line 55
[05-Jun-2026 12:22:55 UTC] ERROR PostmanWpMail: Exception code=0 message=Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}
[05-Jun-2026 12:23:13 UTC] PHP Warning: file_get_contents(/home/ripleysgcco/public_html/wp-content/uploads/voucherpdfuploads/17806620119846836680335648-receipt.pdf): Failed to open stream: No such file or directory in /home/ripleysgcco/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanPostmarkMailEngine.php on line 55
[05-Jun-2026 12:23:14 UTC] ERROR PostmanWpMail: Exception code=0 message=Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}
[05-Jun-2026 12:23:18 UTC] PHP Warning: file_get_contents(/home/ripleysgcco/public_html/wp-content/uploads/voucherpdfuploads/17806620119846836680335648-receipt.pdf): Failed to open stream: No such file or directory in /home/ripleysgcco/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanPostmarkMailEngine.php on line 55
[05-Jun-2026 12:23:18 UTC] ERROR PostmanWpMail: Exception code=0 message=Code: 422, Message: Unprocessable Entity, Body: {“ErrorCode”:300,”Message”:”Zero-sized attachments not allowed.”}

For sending of e-mails, we use the Post SMTP plugin and the postmarkapp.com service.

Hopefully that all helps but if you need anything else, please just let me know.

Viewing 2 replies - 1 through 2 (of 2 total)

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