Error: "[MailKit.Security.AuthenticationException] AuthenticationInvalidCredentials: #5.7.0 Authentication failed." (4322798)

When using the mail server solution "Cisco Secure Email Gateway", authentication fails if the credentials contain a domain name.

Emails are not sent, and frozen jobs occur. The JobService.log shows the following error:

[MailKit.Security.AuthenticationException] AuthenticationInvalidCredentials: #5.7.0 Authentication failed
       at StdioProcessor.StdioProcessor._Execute(Job job)
       at VI.JobService.JobComponents.MailComponent.Activate(String task)
       at VI.JobService.JobComponents.MailComponent._SendRichMail()
       at VI.JobService.JobComponents.MailComponent._Send(MimeMessage message, MailSecurity security)
       at VI.JobService.JobComponents.MailComponent._GetOrOpenSmtpConnection()
       at MailKit.Net.Smtp.SmtpClient.Authenticate(Encoding encoding, ICredentials credentials, CancellationToken cancellationToken)

Corresponding entries can be found in the Mail Server log:

Tue Nov 23 13:29:41 2021 Info: SMTP Auth: (ICID 1120550) failed for user: smtp_account using AUTH mechanism: PLAIN with profile: SMTP_AUTH_LDAP
Tue Nov 23 13:29:42 2021 Info: SMTP Auth: (ICID 1120550) failed for user: smtp_account using AUTH mechanism: LOGIN with profile: SMTP_AUTH_LDAP

You can see here that the user " smtp_account " is authenticated by the mail server without a domain name, although the JobRun parameter "Domain" is populated:

2021-12-15 17:11:05.7996 DEBUG (JobGenLog 2ba913cc-e808-46ef-bc3e-163b71f376f6) : Parameter Domain: ‘smtp_domain.tld’

This is obviously a problem with the mail server solution "Cisco Secure Email Gateway".

The config param 'SMTPDomain' should be deactivated and the complete name "smpt_account@smtp_domain.tld" should be stored in the CP 'SMTPAccount'.