This is fixed in version 6.28rc20. Thanks a lot MikroTik!
Thank you, version 6.28 did correct the short smtp connection timeout problem. However, other short timeouts now exist within the communication session. On high latency connections (or those with intentional anti-spam post-connection delays), if RouterOS 's e-mail tool does not receive a reply within 15 seconds, it will abort the session without generating any error message or attempting a retry. This specific problem only popped up in 6.28.
A 15 second response delay appears to be enough to trigger the behavior. This can be duplicated by configuring a Postfix based mail server using the "sleep" directive. For example the e-mail tool will drop out (without generating syslog error messages) after sending "RCPT TO:" with the remote Postfix mail server configured as follows:
This is not a critical problem (since removing the sleep line resolves the problem); however, it does introduce a new, undesirable behavior. Increasing the time-out or adding a debug syslog event would be most useful.
Thanks again for fixing the original connection timeout bug