Server Closes Connection Unexpectedly

Hi Support,

Thanks for the free plugin.

I am currently experiencing a strange issue where the server is closing the connection prior to any mail being sent. There appears to be no verification issue, or readable errors that I can see. It’s very strange indeed.

Server Info:
OS: Linux srv2200.local.ltd 2.6.32-504.30.3.el6.x86_64 #1 SMP Wed Jul 15 10:13:09 UTC 2015 x86_64
PHP version: 5.6.31
WordPress version: 4.8.2
WordPress multisite: Yes
openssl: Available
allow_url_fopen: Enabled
stream_socket_client: Available
fsockopen: Available
cURL: Available
cURL Version: 7.38.0, OpenSSL/1.0.1e

Output from test email: (I have replaced our server IP and domain with placeholders)

2017-09-20 14:32:05 Connection: opening to ssl://smtp.gmail.com:465, timeout=300, options=array ( ‘ssl’ => array ( ‘verify_peer’ => false, ‘verify_peer_name’ => false, ‘allow_self_signed’ => true, ),)
2017-09-20 14:32:05 Connection: opened
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “220 smtp.gmail.com ESMTP t4sm941993edc.42 – gsmtp”
2017-09-20 14:32:05 SERVER -> CLIENT: 220 smtp.gmail.com ESMTP t4sm941993edc.42 – gsmtp
2017-09-20 14:32:05 CLIENT -> SERVER: EHLO mydomain.com
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-smtp.gmail.com at your service, [1.2.3.4]”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-SIZE 35882577”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-8BITMIME”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-ENHANCEDSTATUSCODES”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH250-ENHANCEDSTATUSCODES”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-PIPELINING”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH250-ENHANCEDSTATUSCODES250-PIPELINING”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250-CHUNKING”
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH250-ENHANCEDSTATUSCODES250-PIPELINING250-CHUNKING”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “250 SMTPUTF8”
2017-09-20 14:32:05 SERVER -> CLIENT: 250-smtp.gmail.com at your service, [1.2.3.4]250-SIZE 35882577250-8BITMIME250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH250-ENHANCEDSTATUSCODES250-PIPELINING250-CHUNKING250 SMTPUTF8
2017-09-20 14:32:05 Auth method requested: XOAUTH2
2017-09-20 14:32:05 Auth methods available on the server: LOGIN,PLAIN,XOAUTH2,PLAIN-CLIENTTOKEN,OAUTHBEARER,XOAUTH
2017-09-20 14:32:05 CLIENT -> SERVER: QUIT
2017-09-20 14:32:05 SMTP -> get_lines(): $data is “”
2017-09-20 14:32:05 SMTP -> get_lines(): $str is “221 2.0.0 closing connection t4sm941993edc.42 – gsmtp”
2017-09-20 14:32:05 SERVER -> CLIENT: 221 2.0.0 closing connection t4sm941993edc.42 – gsmtp
2017-09-20 14:32:05 Connection: closed

I have tried both SSL and TLS, also revoking + reauthenticating the permissions.

Please advise – thanks.