Recently, during the migration of one of our sites to ColdFusion 2023, an unexpected error cropped up, causing around 30% of bulk emails to go undelivered. When attempting to resend these emails, a peculiar pattern emerged – the same percentage of undelivered emails persisted, but with different recipients.

In our ColdFusion server, we meticulously configured mail server settings. However, for our transactional emails, we leverage MailSender, which operates through its own SMTP server and can seamlessly integrate with the cfmail tag:

<cfmail from=”SENDER” to=”RECIPIENT” subject=”bulk transactional email”

server=”smtp.mailersend.net”

port=”587″

useTLS=”yes”

username=”username”

password=”password”

> 

Email Body

</cfmail>

Interestingly, there were no issues when using the default SMTP server or when sending individual emails via MailerSend.

Yet, a perplexing error, “com.sun.mail.smtp.SMTPSendFailedException: [EOF],” surfaced when using MailSender for bulk emails.

A quick search led to suggestions recommending a ColdFusion reinstallation, which I wanted to avoid if possible.

Undeterred, I delved deeper into the issue, exploring potential solutions without resorting to a ColdFusion or Java update. Experimenting with the Mail settings in the ColdFusion admin panel, I discovered that unchecking the recommended ‘Maintain connection to mail server’ setting miraculously resolved the problem.

This experience underscores the importance of exploring various avenues when troubleshooting technical glitches, as solutions might emerge from unexpected quarters. If you’ve encountered a similar issue, give this adjustment a try before considering more drastic measures like a full reinstallation.