Roundcube - Connection Error (Failed to reach server)

Logged in to user control panel. Use auto login to roundcube

Email 1 - Try sending email I get the error  "Connection Error (Failed to reach server)"

Other 9 email ids works flawlessly

Please suggest

Error logs say

[05-Dec-2025 11:05:13 +0000]: <g9kaaxsd> IMAP Error: Login failed for user@dom                                                                             
ain.tld against localhost from 127.0.0.1 (X-Real-IP: 59.93.x.y,X-Forwarded-F                                                                             
or: 59.93.x.y, 59.93.x.y). AUTHENTICATE PLAIN: Authentication failed. in /                                                                             
usr/local/cwpsrv/var/services/roundcube/program/lib/Roundcube/rcube_imap.php on   
line 211 (POST /?_task=login&_action=login)

                                                                         

Make sure you have the IMAP option enabled when you built PHP.

If it's automated login from the panel, should be using an API key to authenticate. Could be an odd gremlin. Try logging out/logging back in. Or could be some specific problem with the account. Can you test logging in manually? Are you able to reset the user credentials without interrupting customer access?

Also what version of PHP and OS are you running?