As you allow to select from multiple domais to login, there is a need to also have an array of Domains that are allowed as SMTP corresponding to the Login Domain. Many servers do not allow mail relay from other domains. Right now there are two options

MAIL()

or

A fixed SMTP relay server

There is no way to select multiple SMTP, as there is for Login. If you have two possible login domains (i.e. mail.domain1.com & mail.domain2.com) you should be able to send (SMTP) mail through SMTP mail.domain1.com if logged using this domain and so on.

There is thight security now a days regarding mail relay, this feature might come in handy. If this already exist, share how please, it is useful

Great Work !


regards