If your system cannot relay mail correctly already, as most office setups are easy to configure to be able to provide that without extra config, at least for Linux setups, then the set up means having something like the following in their gitconfig:
FWIW, I haven't done that kind of setup for years because modern iOS/macOS does email server discovery, where you enter "bob@example.com" and then it does discovery and figures out the right imap.example.com:587 etc for you by looking at DNS.
Yes, such things are nice. The well-known URI [0] system is also sometimes used for this, at least there's one entry for Thunderbird under the "autoconfig/mail" subdirectory. Having some of those auto-config methods available for git send-mail could be nice, as it would lower the barrier a bit further, even if most devs are probably able to check their SMTP endpoint and port.
And that has to be done once, iow., in essence it's as hard a setting up an email fat client like thunderbird.