Bitrix24 Self-hosted administration

Email feature in Bitrix24 Cloud version operates with official Bitrix24 mail server. However, Bitrix24 On-premise uses your custom email server. Such server must be configured correctly, with specific sender-associated SMTP server to be used.

Below is the approximate sequence of your actions:

1. Catch all outbound email using the function custom_mail Starting from Bitrix24 version 7.1.3, standard email mechanism can be redefined.
   
   Mechanics are simple: bxmail() function is called anywhere where mail() must be called. Bitrix24 checks inside bxmail() if custom_mail() is defined before calling standard function mail(). Defined custom_mail() replaces mail() function. Accordingly, write the function custom_mail() to redefine sending mechanism.
2. Configure any MTA ( Mail Transfer Agent MTA — minimally required software needed for receiving and sending emails. Any MTA operates simultaneously with several email protocols: SMTP, POP, IMAP.
   
   Learn more... ) email server, suitable for your objectives.
3. Employ previously used function custom_mail, troubleshoot outbound emails via configured email server from the required mailboxes You can manage email records at the Mailboxes page (Services > Mail > Mailboxes). Be advised, that Bitrix Framework allows creating an unlimited number of email entries.