Synology MailPlus Server Administrator's Guide - Based on version 3.3
For DSM 7.2 and above
Chapter 7: Protocol Settings
MailPlus Server provides a centralized configuration interface for mail service protocols. You can open/close ports for certain protocols or rebind the network interface of your server. Since protocol settings affect the external operations of the entire server, make sure the settings are configured according to your needs.
SMTP
The SMTP uses three ports. In MailPlus Server, they are displayed as SMTP (port number: 25), SMTP-SSL (port number: 465), and SMTP-TLS (port number: 587). The three protocols and their respective roles are listed below:
- SMTP: SMTP is a standard protocol used to receive external emails and deliver internal emails. MailPlus Server uses Postfix and will deliver email messages using hamming code when STARTTLS is not specified. Currently, our SMTP is not encrypted. If you need encryption, see here for more information.
- SMTP-SSL: SMTPS is a supported protocol for SMTP-SSL. Since DSM no longer supports SSL encryption, MailPlus Server can only connect to SMTP-SSL through TLS.
- SMTP-STARTTLS: SMTPS is a supported protocol for SMTP-STARTTLS and performs encryption through STARTTLS. SMTP-STARTTLS requires authentication; therefore, it is often used for the internal protocol between client and MSA.
Notes:
- SMTP-SSL is different from encrypting SMTP through STARTTLS. SMTP must send encrypted packets out after a handshake. If you need to relay using this protocol, refer to here for more information.
Set up SMTP
Refer to the following instructions on the configuration of SMTP and respective ports:
- Go to Service > Protocol > SMTP and tick the Enable SMTP checkbox.
- You can change the port number in the Port field.
- You can adjust the following settings:
- Enable SMTP-SSL/TLS: Tick to encrypt the SMTP connection between your MailPlus Server and other email servers or clients with TLS.
- Enable SMTP-STARTTLS: Tick to encrypt the SMTP connection between your MailPlus Server and other email servers or clients with STARTTLS.
- Click Apply to save the settings.
Notes:
- SMTP is the main protocol for a mail server.
- Unless there are special circumstances, we recommend that you use the default port 25.
IMAP/POP3
IMAP/POP3 provides both encrypted and non-encrypted options, thereby using four ports. In MailPlus Server, these ports are IMAP (port number: 143), IMAPS (port number: 993), POP3 (port number: 110), and POP3S (port number: 995). Through these protocols, you can retrieve email information from MailPlus Server using different email clients.
- IMAP: IMAP is a standard protocol that allows users to access data stored on a mail server. IMAP clients modify emails on the mail server, which will be mirrored to all IMAP client mailboxes; therefore, all the changes made to an email will be synchronized across multiple devices.
- POP3: POP3 is a standard protocol that allows users to access data stored on a mail server. POP3 clients download emails from the server and save them locally, so changes made to an email will not be synchronized back to the mail server.
Notes:
- Both protocols encrypt through STARTTLS. Since DSM no longer supports SSL encrypted connection, do not set up SSL for an encrypted connection.
Set up IMAP/POP3
You can refer to the following steps to configure IMAP, POP3, and their respective ports:
- Go to Service > IMAP/POP3.
- You can adjust the following settings under the IMAP/POP3 section:
- Enable POP3: Tick to allow email client software to receive messages using POP3.
- Enable POP3 SSL/TLS: Tick to allow POP3 client connection to be protected with SSL/TLS.
- Enable IMAP: Tick to allow email client software to receive messages using IMAP.
- Enable IMAP SSL/TLS: Tick to allow IMAP client connection to be protected with SSL/TLS.
- Click Apply to save the settings.
Network Interface
After configuring high-availability for MailPlus Server, specify a network interface for internal cluster communication. You can manually configure the network interface to retrieve its IP address.
Modify network interface
- Sign in to DSM and launch MailPlus Server.
- Go to Service > Network Interface and switch network interfaces from the Network Interface drop-down menu.
- Click Apply to save the settings.
