[Dovecot] [Q] auth(default): plain(?, 11.111.206.99): Username contains disallowed character: 0x20

Dear all,

A new user with Microsoft Express is trying to use IMAP SSL port

993. However they cannot log in. Its only with them. The logs details the following:

Feb 11 18:56:03 logout dovecot: auth(default): plain(?,11.111.206.99): Username contains disallowed character: 0x20 Feb 11 18:58:07 logout dovecot: imap-login: Disconnected (auth failed, 1 attempts): method=PLAIN, rip=11.111.206.99, lip=62.58.61.184, TLS: Disconnected

I think that the 0x20 is a space. However the user states that they are using this format and that there is no space: user.name@test.com

Does anyone know where I could start to look for this?

Regards,S