Support custom sender display name for outbound emails

Currently, all outbound emails from Immy just show up in users mailboxes as from the raw address, e.g., “[email protected]”, which looks kind of spammy and not user-friendly. It would be really great if we could have an additional field on the branding page to specify the display name. Having the emails show up as from something like “MSP Maintenance Team” would be a lot friendlier looking in users’ inboxes.