Send from another address (send-as)

Settings → Mailboxes → the mailbox → Send-as addresses. Add the address and a display name; Mailbind emails a 6-digit code to it. Once verified, the address appears in the From picker and replies to mail sent to it go out from it automatically.

Most providers also require the alias to exist on their side (as an alias or a "send mail as" entry), otherwise the server rejects the From header.