Mail Server Settings

Each mail server within an organization has its own settings, found under Settings in the server menu. Some settings are only visible to global administrators under Advanced Settings.

Server settings

Setting	Description
Name	A display name, unique within the organization.
Permalink	A short identifier (letters, digits and hyphens) used in SMTP usernames (org-permalink/server-permalink) and URLs. It cannot be changed after the server is created.
Mode	Live or Development. See below.
IP pool	Only shown when IP pools are enabled. The pool that outgoing mail from this server is sent from unless an IP pool rule matches.
Postmaster	The contact address included in bounce messages Postal generates when an incoming message cannot be delivered. Defaults to postmaster@ the message's domain.

Live and Development mode

In Live mode all mail is routed normally. In Development mode every outgoing and incoming message is placed in the held queue instead of being delivered to recipients or endpoints. Messages are still parsed, inspected and visible in the web interface, and count towards the server's send limit. Individual held messages can be released manually from the web interface, which delivers them despite the mode.

If you only want to hold messages from a particular application or environment rather than the whole server, set the hold option on that application's credential instead.

Spam

The Spam threshold and Spam failure threshold for incoming mail are set here. See Spam & Virus Checking.

Retention

Each server has three retention settings which are shown on the Retention page and can be changed by a global administrator under Advanced Settings. They are enforced by a background task which runs once a day at 03:00 (server time, normally UTC).

Setting	Default	Description
Raw message retention days	30	How many days the raw content of messages (headers, bodies and attachments) is kept. Raw data is stored in one table per day, and whole days are removed once they are older than this. After removal the message still appears in lists and searches but its content and attachments can no longer be viewed, and a queued message whose raw data has been removed will fail with "Raw message has been removed".
Raw message retention size	2048 MB	The total disk space raw message data may use. When exceeded, whole days are removed starting with the oldest until usage is under the limit.
Message retention days	60	How many days message metadata (the message record itself, its deliveries, clicks, loads and spam checks) is kept. Older messages are deleted entirely.

Leaving any of these blank disables that limit ("Indefinitely" / "No limit"). The Retention page also shows the current total size of the server's message database.

Send limit

A global administrator can set a Send limit for a server under Advanced Settings. This is the maximum number of outgoing messages accepted in a rolling 60 minute window; the current usage is shown on the Send Limit page. Incoming messages are counted but not limited.

• When the volume reaches 90% of the limit, the server is marked as approaching its limit.
• When the volume reaches the limit, every further outgoing message is held until the volume drops. Releasing a held message while the server is still over the limit holds it again.

Once a minute Postal checks for servers that have recently approached or exceeded their limit and, at most once per hour for each state, e-mails every user in the organization and triggers the SendLimitApproaching / SendLimitExceeded webhook events. The e-mails are sent using the smtp section of your Postal configuration.

Held messages

Messages that are held are not delivered but remain visible under Messages → Held where they can be released (re-queued for delivery) or the hold cancelled. Each held message triggers a MessageHeld webhook. A message may be held for any of the following reasons:

Reason	Can be released manually?
Server is in Development mode	Yes
Credential is set to hold	Yes
Recipient is on the suppression list	Yes
Send limit reached	Only once the volume has dropped below the limit
Server is suspended	No - it will be held again until unsuspended
Incoming spam on a route set to Quarantine	Yes
Incoming mail on a route set to Hold	Yes (marked as Processed)

Held messages expire after the number of days set by postal.default_maximum_hold_expiry_days (default 7). An hourly task cancels the hold on expired messages, recording a HoldCancelled delivery. The message is not delivered.

Suppression list

Each server maintains a suppression list of recipient addresses that Postal will not deliver to, viewable under Messages → Suppressions. Addresses are added automatically when Postal is sending outgoing mail:

• Too many hard fails - a permanent (5xx) rejection from the recipient's mail server when there has already been at least one other hard fail to the same address in the previous 24 hours.
• Too many soft fails - the message has been retried the maximum number of times (postal.default_maximum_delivery_attempts, default 18) without success.

Incoming bounce messages do not add addresses to the list.

While an address is on the list, new messages to it are held (see above) rather than attempted. Releasing such a message manually bypasses the list, and if the delivery then succeeds the address is removed from the list. Entries are otherwise removed automatically after postal.default_suppression_list_automatic_removal_days (default 30) days.

Advanced settings (administrators only)

Setting	Description
Send limit	See above.
Allow sender header	Permits any From address as long as a Sender header contains an address on one of the server's verified domains. See From/Sender validation. Applies to SMTP and the API.
Privacy mode	When enabled, the Received header Postal adds to submitted messages omits the submitting client's IP address, reverse DNS hostname and HELO name, leaving only by {hostname} with SMTP/HTTP; {date}.
Log SMTP data	Log the full content of messages submitted using this server's credentials in the SMTP server log. Debugging only. See Logging.
Outbound spam threshold	Enables spam scanning of outgoing messages; messages scoring at or above this are failed. Blank disables outbound scanning. See Spam & Virus Checking.
Message retention days, Raw message retention days, Raw message retention size	See Retention.

Suspending a server

An administrator can suspend a server from Advanced Settings by entering a reason. While suspended:

• Every message processed for the server (incoming and outgoing) is held with the reason "Mail server has been suspended".
• The SMTP server rejects RCPT TO for the server's routes and credentials with 535 Mail server has been suspended.
• API requests using the server's credentials return the ServerSuspended error.
• All users in the organization are e-mailed about the suspension.

Use Unsuspend server to restore normal operation; held messages must then be released manually.

Deleting a server

Deleting a server (Settings → Delete, which requires typing the server's name to confirm) marks it as deleted immediately and hides it from the interface. The server's message database is dropped by an hourly background task shortly afterwards. This cannot be undone.