Bugfix: #93635 - Add mail configuration for setting smtp domain

See Issue #93635

Description

Some smtp-relay-server require to set the domain under which the sender is sending a email. As default the EsmtpTransport from Symfony will use the current domain/IP of the host or container. This will be sufficient for the most of the servers but some servers requires a valid domain is passed. If this isn’t done, sending emails via such servers will fail.

Setting a valid smtp domain can be achieved by setting ['MAIL']['transport_smtp_domain'] in the LocalConfiguration.php. This will set the given domain to the EsmtpTransport agent an send the correct EHLO-command to the relay-server.

Configuration Example for GSuite.

Impact

Now it is possible to set the smtp mail domain which is required for some relay-server.