I had a perfectly working installation of Roundcube 1.0.1.
Since last Friday none of the users were able to send email through Roundcube.
The following error message pops up:
SMTP Error 550: Failed to set sender "xxxx@domain.com" (SECURITY: Local connection with invalid mail from credentials.)
Where xxxx@domain.com is the actual sender's email address.
The email account otherwise works with POP or IMAP setup, only this installation of Roundcube has this error. None of the users reached their storage quota and this is a low overall volume account.
Any help is appreciated. This is not a new install - no idea what happened...