MailPlus Server provides a privately hosted mail service on Synology NAS, with centralized domain administration, security, high availability, and migration capabilities.
Application component
Synology MailPlus Server
Overview
Monitoring
Administrators can monitor:
- Outgoing mail sent, resent, or unable to be sent.
- Incoming mail received or rejected.
- Real-time server information, including high-availability cluster status.
- Email threat statistics in graphs.
- Statistics of blocked inbound and outbound mail, including top senders and recipients.
- Mail server information through SNMP, including delivery results, security events, mail queue, IMAP/POP3/SMTP connections, and Postfix/Dovecot service statuses. (SNMP MIB Guide)
Domain and Mail Service Management
Domain and Mail Flow Controls
- Administrators can manage multiple domains and configure aliases, auto BCC, usage limits, and disclaimers.
- Domain sharing allows multiple MailPlus Server instances to share one email domain while server management remains independent.
- SMTP authentication requires clients to provide credentials when connecting to MailPlus Server through SMTP.
- SMTP settings define the hostname and SMTP banner, and set limits on the number of recipients per mail, mail hops, and mail size.
- External postmaster can receive system mail sent to Mailer-daemon and postmaster aliases from other mail servers.
- Mail can be delivered through other mail servers to reduce direct Internet exposure of mail content.
- MailPlus Server can relay mail for trusted servers and listed domains.
- Block and allow lists can reject, discard, or accept mail that matches configured criteria.
- Connection policies can block mail from unidentifiable domains or hosts that may overload MailPlus Server.
- External mail servers and third-party clients can communicate with MailPlus Server through SMTP, POP3, and IMAP.
Mailbox Administration
- Mailbox quotas and quota notifications help control data growth.
- The management console shows mailbox size and user status.
- Deactivated users' mailboxes can be deleted in batches.
- User mailbox data can be imported in SMC or PST format.
- User mailboxes can be exported to PST files.
High Availability
- MailPlus Server can use a high-availability structure to keep mail service available during system updates and hardware replacements by switching service to the paired server in seconds.
Mail Security and Threat Protection
Anti-spam, Antivirus, and Mail Protection
- Custom spam filtering rules work with auto-learning.
- The Rspamd anti-spam engine provides anti-spam protection.
- DNSBL filters spam based on listed IP addresses of computers or networks.
- Greylist returns temporary errors to mail clients.
- ClamAV and the optional paid McAfee antivirus engine scan incoming and outgoing mail for viruses. When mail is found infected, MailPlus Server can delete or quarantine the message and notify intended recipients
- ClamAV antivirus engine databases, such as Google SafeBrowsing or third-party databases, help detect malicious links in mail.
- Virus definitions can be updated automatically on a custom schedule.
- Authentication mechanisms including SPF, DKIM, DMARC, and DANE help guard against spam and identity theft.
- Mail can be filtered by potentially dangerous content and attachment file types.
- Message Content Protection (MCP) rules can filter or block targeted mail. When the total MCP score of matched rules exceeds the configured threshold, MailPlus Server performs the selected action: save to quarantine, deliver anyway, delete mail, notify the sender, or forward.
- Email moderation allows authorized users to review and approval before delivery.
Requirements
- Models with at least 2 GB RAM are recommended for smooth security engine operation.
Auditing
| Log or function | Coverage |
|---|---|
| Transaction logs | Sent and received mail, spam detection, message delivery, and error notifications |
| Client access logs | Client-side connections, mail operations, and authentication processes |
| Admin logs | Setting changes made by administrators |
| Log management | Archiving, transferring, rotating logs, and generating daily reports |
| Keyword search | Deleting and exporting specific mail |
Mail Migration
Supported Migration Sources
| Source | Source-specific note |
|---|---|
| Gmail | Gmail mail can be migrated per label while keeping the original structure intact |
| Google Workspace | |
| Microsoft Exchange | Exchange system configurations can be reused for quick system replacement |
| Yahoo | N/A |
| Other IMAP servers | N/A |
Migration Controls
- Multiple migration tasks can be created for external mail servers,with filters to bypass spam, mail received after a specified date, and mail exceeding the configured size limit.
- Exchange migration can avoid asking each source Exchange user for access permission when a delegated account is available.
Server Sizing
| Metric | Listed maximum |
|---|---|
| Concurrent users | 4,000 |
| Emails processed per day | 5,721,000 |
Limitation
- User limits and processed-mail limits vary by Synology NAS model. Refer to product specifications or the Synology MailPlus license page for model-specific details.
Synology MailPlus Web Client
Compose and Send
- Recipient suggestions use email addresses saved in Synology Contacts.
- Drafts are saved automatically.
- S/MIME and OpenPGP provide mail encryption and signing.
- Send cancellation windows can be set to 5, 10, 15, 20, or 30 seconds.
- Text styling includes font style, font size, and color.
- Users can configure auto-replies and auto-forwarding.
- Scheduled sending delivers mail at a selected date and time.
- Mail merge creates personalized mass mail. (Learn more)
- Mail templates store reusable text and images.
- Mail tracking is available through delivery and read receipts
Mail Management
Organization and Mailboxes
- Priority mailbox collects mail from different mailboxes or labels.
- Nested labels support hierarchical classification.
- Filters can include custom exception rules.
- Mails can be starred, archived, moved to custom mailboxes, or labeled.
- Shared mailboxes can be assigned to internal users and groups with specific access permissions.
- Archived mailboxes can display archived mails.
View, Search, and Preview
- Two-column and three-column split panes are available. Two-column mode includes one-line layouts with or without a preview and a two-line layout.
- Universal search supports syntax operators.
- External images can be displayed automatically or only after confirmation.
- Browser push notifications are available.
- Mail can be displayed as individual messages or in conversation mode, which groups a message with its replies.
- Mailbox usage and storage-limit warnings are shown.
- Supported attachment formats can be previewed through Universal Viewer.
General Settings and External Servers
- Multiple signatures can be prepared for different scenarios.
- Conversations wrongly identified as spam can be restored.
- Users can add or edit additional SMTP servers, such as Google SMTP with the required account credentials.
- Mail can be fetched from custom POP3 servers or predefined POP3 servers such as Gmail.
Administrator-controlled Features
Administrators can allow users to:
- Receive mail from external POP3 servers.
- Share links for large attachments.
- Use S/MIME or OpenPGP to encrypt and sign mail.
- Customize the MailPlus web portal logo.
- Export mailboxes to PST files, subject to the email export policy configured in MailPlus Server.
Synology Integration
- Synology Chat and Synology Calendar plug-ins connect MailPlus with project discussions and to-do workflows.
- MailPlus conversations can be added as tasks in Synology Calendar.
Requirements
- Synology Chat or Synology Calendar is required.
AI Features
- Summarize mail threads for a quick overview.
- Assists with drafting and refining mail in the composer.
Requirements
- Synology AI Console must be set up.
Affiliated Utility
Synology MailPlus (Mobile)
System Requirements
| Feature area | iOS | Android |
|---|---|---|
| MailPlus Mobile | 17.0 or above | 10 or above |
| Calendar features | 17.0 or above | 10 or above |
Email Management
- Conversation view supports mobile mail browsing.
- Mail can be labeled, moved to a specific mailbox, starred, or marked as read, or unread.
- Scheduled delivery sends mail by selected date and time.
- Localized email addresses allow mail to be sent from or received by addresses in native languages, such as Chinese and Russian.
- Swipe gestures for moving across the next or previous email thread.
- Actions on email notifications: delete, archive, and mark as read.
- Undo is available for the labeled actions: delete, move, archive, and remove.
- Messages can be printed from a mail thread.
- Attached images can be viewed without downloading.
- Calendar events received by email can be manually added to Synology Calendar.
- Events can be manually added to Synology Calendar.
Calendar Management
Browsing and Display
- Calendar views include Day, Month, and Agenda.
- Display options include My Calendar and Other Calendars.
- Event display options include hidden events and declined events.
Event Actions and Notifications
- Events can be viewed, created, edited, and deleted.
- Event reminders can be sent at specified times.
- Events can be hidden or unhidden.
- Notifications can be enabled for all events.
- Daily summaries highlight important events.
Security
- Passcode lock protects mobile data, and Touch ID is supported on compatible devices.
- OpenPGP provides mail encryption and decryption.
- Suspicious mail can be reported to the system administrator to improve spam learning.
Settings and Integrations
- Users can switch accounts and receive notifications from multiple accounts without signing in repeatedly.
- Swipe actions can be customized for delete, archive, Spam/Not Spam, read/unread, labels, and move-to-mailbox behavior.
- Display settings include preview lines, font size, and dark theme.
- Push notifications can be enabled for user-defined mailboxes.
- Composition settings include mobile signatures, templates, and auto-reply.
- Built-in stickers and emoji are available for quick replies.
- Remote-content settings include automatic remote-image loading and Wi-Fi-only mail content prefetch.
- Mailboxes and labels can be created, edited, and deleted.
- Priority mailbox can be enabled with settings based on the web client.
- Shared links can open directly in Synology Drive on mobile instead of the default browser.
- Image and attachment cache storage can be limited.
- Calendar settings include enabling Synology Calendar, calendar notifications, daily summaries, the first day of the week, and week number display.
- MailPlus Mobile can also integrate with other calendar applications.
AI Features
- MailPlus Mobile can summarize mail threads and assist with drafting and refining mail in the composer.
Requirements
- Synology AI Console must be set up.
- AI features must be enabled in the MailPlus web client.