Why a cold IP gets filtered even with clean content
Mailbox providers weigh sending IP reputation heavily, and a brand-new IP has no history at all — no baseline of how recipients respond to mail from it. A sudden burst of high volume from an IP with zero sending history looks statistically identical to the start of a spam run, regardless of how legitimate the actual content is, which is why providers apply heavier filtering to unfamiliar IPs by default.
What a warming schedule actually does
A warming plan starts at a small daily volume — often just a few hundred messages — sent to the most engaged, most likely-to-open portion of a list, and increases volume incrementally over roughly two to four weeks as positive engagement (opens, replies, low complaints) accumulates. The goal is giving mailbox providers a growing, positive signal to attach to the IP before it ever needs to carry peak volume.
This mostly matters for dedicated IPs
A shared IP pool, like SES's default sending infrastructure, already carries an aggregate reputation built from every sender using it, so a new account sending through it doesn't start from zero the way a freshly provisioned dedicated IP does. Warming is primarily a dedicated-IP concern — it's the price of owning your own reputation rather than borrowing a pool's established one.
Sending to your worst engagement segment first undoes it
Warming works because it front-loads positive signal onto an unproven IP. Sending a re-engagement campaign, a purchased list, or any low-engagement segment during the warming window does the opposite of what warming is for — it attaches the negative signal that's most damaging precisely to the IP that has the least existing reputation to absorb it.
Why it matters
Skipping IP warming on a new dedicated IP is one of the most common ways a deliverability problem gets self-inflicted right at launch — the technical setup (SPF, DKIM, DMARC) can be perfect and the IP still gets aggressively filtered simply because mailbox providers have no reason yet to trust it at volume.
Common questions
How long does IP warming take?
Typically two to four weeks, starting at a low daily volume sent to the most engaged subscribers and increasing incrementally as positive engagement accumulates, rather than a fixed schedule that applies identically to every sender.
Do I need to warm up SES's shared sending IPs?
No. Shared IP pools already carry an aggregate reputation built from every sender using them, so a new account doesn't start from zero the way a freshly provisioned dedicated IP does. Warming is a dedicated-IP concern.
What happens if I send to a low-engagement list during IP warming?
It undermines the entire point. Warming works by attaching positive signal to an unproven IP first — sending to a stale or purchased list during that window attaches negative signal precisely when the IP has the least reputation built up to absorb it.