I have tested on two installations, our own server running 2.6.4-lts 170202 and a test server on Limeservice using 2.62.1

In both instances, when sending email via the Elasticemail SMTP service (https://elasticemail.com/), the SMTP connection fails. This appears to be as a consequence of the recent update to use version 5.2.22 of phpmailer.

We have a Wordpress installation that has also been recently updated to phpmailer 5.2.22, but that can still send email via Elasticemail. It therefore seems to be the way in which Limesurvey is using phpmailer, rather than 5.2.22 itself.

By replacing the phpmailer directory in our 2.6.4 lts 170202 build with the older version from before the update (this uses phpmailer 5.2.8) , I have been able to get email working again as a short term solution. However, phpmailer 5.2.22 patches a high priority security vulnerability, so the rollback solution can only be temporary.

The full phpmailer error message is provided in the additional information field below. Identifiers have been redacted. Having been in discussion with Elasticemail technical support, on first glance they suspect that the credentials are getting corrupted or truncated. Note that Elasticemail uses 36 character SMTP passwords (and optionally the same length username).