[bug-mailutils] Trouble with 'mail' on Raspberry Pi's

[BoLoPoFs RPi05]

Dear Sir/Madame,

I need to ask one simple question, and hope I'm allowed to. I'm running 
'mail' at several Raspberry Pi's, and have it good working with many of 
my mail accounts. But there is one mode of failure;

When I configure '/etc/ssmtp/ssmtp.conf' with AuthUser=mj432987 (which 
is the form of user name of my account) it will work, but other e-mail 
accounts just have the e-mail address as the user name (for example 
'address@hidden') and then it will not work even with my 
otherwise working account. The error flag will be set to 36. My simple 
suspicion is that the character '@' and or '.' not will be sent by mail, 
but I'm not able to check that.

Is this something known in 'mail', or is it known of some other reason? 
I have tried the OS Raspian Whezzy as well as the new Raspbian Buster, 
even recently upgraded.

I would be really thankful if You can help me further in this question.

Best regards
Lars Nordin
Täby - Sweden

(I'm sorry for the strange name as the sender of this mail, but it is 
sent from one ofthe mailboxes I use on the Raspberry Pi's).