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PMTA knowledge base›Block <domain>›Directive§ 3.3.10.89

smtp-out-rampup-interval

<domain>set by the Hub

The minimum pause before opening the next connection of this queue
in the configuration this is a linesmtp-out-rampup-interval 1sinside the block <domain>
A pause before opening the next connection

The minimum interval between opening connections for one queue. With a value of 1s, a node allowed fifteen connections will open them not in a burst but over fifteen seconds.

This is smoothing, not a limit. The total number of connections is set by max-smtp-out, while this directive decides how fast it is reached. The difference is visible to the recipient: fifteen connections appearing within a second and the same fifteen over a quarter of a minute are different events in its logs.

The main trap. The value multiplies by the number of connections and gives a delay before reaching the full rate. Five seconds with forty connections is more than three minutes of ramp-up, and on short batches the queue will run out before the node reaches the allowed speed.
What the Hub does. It writes it from the node preset: “Careful” — two seconds, “Balanced” — one, “Aggressive” has no such line. It is not written for addresses under warm-up: they have a single connection. The value is always chosen together with max-smtp-out: what matters is their product, not each on its own.
Recommended values
Mode Per address (vMTA) In the provider rule When this is your case
Warm-up, cold address 5s — An address younger than 4–6 weeks or back from a pause
Careful 2s — Strict receivers, questionable reputation, the first weeks after warm-up
Balanced default 1s — Normal operation of an established fleet
Aggressive — Warmed-up addresses, friendly receivers, urgent volumes
PowerMTA default 0 — If the directive is not written at all

Seconds, not minutes. The point is to spread the opening of connections over time, not to delay sending. A second with fifteen connections is fifteen seconds to reach the full rate; five seconds with forty is already more than three minutes, and that is noticeable.

It is needed most during warm-up. A burst of connections harms a young address more than a mature one: the receiver has no history to judge by. Later the value can be lowered.

The default is 0 — connections are opened as fast as the other limits allow.

The order of magnitude is our recommendation, tested on the fleet. From the manual here come the 0 default and the purpose: reduce the number of connections needed and not hit the limit.
Example configuration
# a soft start is noticeable only together with the number of connections
<domain hotmail.com>
    max-smtp-out 15
    smtp-out-rampup-interval 1s</domain>
Fifteen connections with a one-second pause open over fifteen seconds. Without the pause the receiver would see them all at once — the pattern it reacts to most sharply.
yellow — — directive names, blue — blocks. They are highlighted the same way in the text of the card.
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Common mistakes and problems

what people get wrong and how it ends2 mistakes▶

Setting the pause in tens of seconds

our experience

What it costsThe value multiplies by the number of connections. Five seconds with forty connections is more than three minutes to full rate, and on short mailings the queue never gets there.
How to spot itThe mailing ends before the number of connections reaches the allowed one.
How to do it rightKeep the pause within a second or two, and during warm-up up to five, where the number of connections is in single digits anyway.

Setting a pause instead of limiting the rate

our experience

What it costsThe pause spreads connections over time but does not limit their number: a minute later there will still be as many as allowed. As a means of “not opening many,” it does not work.
How to spot itThe number of connections is the same as without the pause — it just builds up more slowly.
How to do it rightLimit the number with max-smtp-out, the opening rate with max-connect-rate. The pause only smooths the start.
Compatibility
PowerMTA 6.0
described in the manual of this version · platform: any
The vendor does not state the first version for every directive — there is no note here. The name also appears in the 5.0 edition of the manual.
Reference data
Syntax
smtp-out-rampup-interval <time-interval>
Values
a time interval; the default is 0 — no pauses
Default
0 § 3.3.10.89
Applying
reload, no restart needed
Queue
will not touch what is already queued
Where to write it
<domain>
How many times
once in the block
Everything here comes from the manual, with the section.
Inheritance
The value merges across <domain> blocks from general to specific: the best-matching block wins, not the last one in the file. It is picked up by pmta reload, no restart needed.
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Related directives

3 relations

Depends on

max-smtp-out<domain>How many connections the pause is spread across: their number determines how long reaching the full rate takes. inference

Works together with

connection-idle-timeout<domain>The flip side: the pause slows down opening new connections, keeping them open removes the need to open them again. § 3.3.10.89

Can be replaced by

max-connect-rate<domain>The pause spreads connections over time, the connection rate limits their number — together they shape the ramp-up to full speed. § 3.3.10.89

How to check on the node
The effective value is printed by the queue settings command; the effect itself is visible from how quickly the number of connections grows after messages appear:
pmta show settings hotmail.com/vmta1 | grep -i rampup
pmta show queues --maxitems=20
If there are consistently fewer connections than the allowed ceiling with a full queue, the pause is probably too long and the queue simply does not have time to reach the rate. The Hub picks the value itself together with the rate.
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What else to read

3 articles

◇Four value types the whole config is written inBoolean, domain pattern, regular expression and time interval — defined once in § 3.2 and then used by all directives.◇How the policy for a receiver is assembledSettings are assembled from the most general pattern to the most precise; the order of blocks in the file means nothing.◇Backoff mode — the queue's second personalityA queue that a receiver has started refusing switches to a parallel set of limits, retries and routes — ten directives that act only in this mode.

In the Hub
Managed at
Configurations → Delivery limits
Value
The Hub picks it itself — pace, warm-up stage, metrics
Cost of a mistake
reversible: harms only while it is set
Scenarios
Tune the pace for a provider
Neighboring settings of the block <domain>:max-smtp-outmax-msg-ratemax-connect-ratebackoff-max-smtp-outbackoff-max-msg-rateAll 135 directives of the block →