Server-wide mail settings

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General options

Installed mail server
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Installed IMAP/POP3 server
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Used by email clients and in MX records. It needs an A record to this server; its TLS certificate is issued automatically.
KBytes
Messages larger than this (text and attachments together) are refused. 0 means unlimited.
The maximum number of mail users that can be logged in at the same time.
The maximum number of connections (IMAP, POP3, IMAP or POP3 over SSL/TLS) of a mail user from one IP address.
Outgoing mail mode
If you select None, outgoing mail is not sent over that protocol (for example, when the IPv6 address has no reverse DNS record).
Clients on ports 110/143 must use STARTTLS before logging in (PCI compliance). Ports 993/995 are always encrypted.
Users can receive mail at addresses like name+tag@example.com, delivered to name@example.com.
Mail users get a message when their mailbox is 95% full.
Customize the mailbox quota warning

Mail autodiscover

Thunderbird, Outlook and phones find the mail server settings by themselves (autoconfig.<domain>, autodiscover.<domain>).
The incoming and outgoing mail server given to mail clients instead of each domain's own. It must have a valid SSL/TLS certificate. Leave it empty to use each domain's.

Relay options

Relaying
min
On port 25 a computer may send to other servers after logging in with SMTP, or for the given minutes after a POP3/IMAP login from the same address. Closed: only the networks of the White List. Ports 587 and 465 always require login.

Limitations on outgoing email messages

The limits themselves are set in the service plans, the subscriptions and the mailboxes. Statistics: Outgoing Mail Control

When off, no limit applies anywhere (the counts are still kept). The change applies within a minute.
One message sent to 10 recipients counts as 10 messages.
The period of the rejections shown in Outgoing Mail Control.
A notification about the attempts to exceed the limits, at most once in this period. Who gets it: Notifications
The limits are set in

DMARC

Incoming mail is checked against the sender domain's DMARC policy (quarantine: marked as spam, reject: refused). Needs the DKIM and SPF checks of incoming mail.

DKIM spam protection

Outgoing mail of the domains is signed with DKIM.
It cannot be switched off while DMARC is switched on.

SPF spam protection

It cannot be switched off while DMARC is switched on.
Each mode also includes the ones above it. Mail of logged-in users and of the White List is not checked.
SPF terms checked before the sender domain's own "all" (for example, trusted forwarders): include:, ip4:, ip6:, a, mx, ptr, exists:.
The SPF record used for senders whose domain has none, starting with v=spf1. Leave it empty for no guess.
The text that the sending server receives when a message is rejected. Latin letters, digits and basic punctuation only.

Spam protection based on DNS blackhole lists

Separate them with a semicolon, for example: zen.spamhaus.org; bl.spamcop.net. Mail from listed servers is refused (550).

Extra auto-reply headers

Headers added to every auto-reply sent from this server, for example X-Auto-Response-Suppress: All.

Extra headers
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