Warming up a domain or SES account

Mailbox providers such as Gmail, Outlook and Yahoo judge mail by the reputation of the sending domain and the IP addresses it comes from. A domain or account with no history that suddenly sends tens of thousands of emails looks like a spammer, so mail lands in spam or is throttled. Warming up means building that history gradually: sending to your most engaged readers first and raising the volume over two to four weeks.

Turn on automatic warm-up on the ESP and SendLit does both for you, or set a daily send limit and raise it by hand.

Do you need to warm up?

Usually less than you fear, if you keep what already has a reputation:

• Same sending domain. Gmail and Outlook weigh domain reputation heavily. If you sent from news.example.com with SPF, DKIM and DMARC set up on your old platform (beehiiv, Mailchimp, Substack custom domains), keep sending from that domain. Its history comes with you.
• Same ESP account or IP. If you already send through your own Amazon SES, Postmark, SendGrid or Mailgun account, connect that account to SendLit. Nothing about your sending infrastructure changes.
• A clean list. Import your list with its statuses so unsubscribed, bounced and complained addresses stay suppressed (see Import contacts).

You do need to warm up when you move to a new domain, a new Amazon SES account or a new dedicated IP, or when your list is much bigger than what you sent before. Even with an existing domain, a new SES account's shared IPs and quota benefit from a short ramp.

Amazon SES before you start

• Leave the sandbox. New SES accounts can only send to verified addresses. In the SES console, request production access for your region, describing your newsletter, how people subscribe and how you handle bounces and complaints.
• Check your quotas. SES gives each account a daily sending quota (Max24HourSend) and a maximum send rate per second (MaxSendRate). Set the ESP's Max send rate in SendLit to your account's MaxSendRate (see Send rate), and ask AWS for a higher daily quota before your list outgrows it.
• Send bounces and complaints back to SendLit, so bad addresses are suppressed straight away. See Amazon SES bounces and complaints.
• Authenticate your domain with SPF, DKIM and DMARC, and verify it in SES.

Automatic warm-up

Open Settings → Email service providers, edit the ESP, turn on Automatic warm-up and enter the number of emails a day you want to grow to (your usual broadcast size, for example). From that day on, SendLit caps the broadcast and sequence emails sent through the ESP each UTC day:

After day 16 the limit grows 40% a day. It stops at your target, and the warm-up ends there. The ESP list shows the day and today's count.

Emails over the day's limit wait for the next day, so a large broadcast goes out over several days. The most engaged contacts go first (see below), so the early days build the reputation that the rest of the list benefits from. Transactional email is never held back.

If you also set a daily send limit, the lower of the two applies. Changing the target keeps the warm-up's progress; turning it off removes the cap. Over the API, set warmupTargetDailyVolume with PATCH /settings/esps/{espId} or the MCP update_esp tool (null turns it off); the ESP's warmup field shows the day and today's limit.

Set a daily send limit

Open Settings → Email service providers, edit the ESP and set Daily send limit for warm-up. It caps how many broadcast and sequence emails go through that ESP per UTC day. Emails over the cap aren't lost or marked failed: they wait and go out from midnight UTC, and a large broadcast simply takes several days. Transactional email (sign-in codes, receipts) is never held back. The ESP list shows today's count against the limit.

Raise the limit every day or two as long as bounces and complaints stay low, and clear it once you're sending your full volume. You can also set it with PATCH /settings/esps/{espId} (dailySendLimit, or null to remove it) or the MCP update_esp tool.

A sample manual ramp

If you'd rather ramp by hand, adjust these steps to your list size; stop raising the limit if bounce or complaint rates climb.

Send to your most engaged readers first

Early sends should go to people who open and click, because their engagement builds reputation fastest. When a broadcast can't go to everyone today, SendLit sends in this order:

1. contacts who clicked recently (a click counts more than an open);
2. contacts who opened recently;
3. contacts with a high open or click rate imported from your old platform (custom fields such as open_rate or click_rate, from a beehiiv or Mailchimp export; see Import contacts);
4. everyone else, newest signups first.

Long inactive readers are sent to last. Consider leaving them out of the audience altogether.

Watch the numbers

• Bounces: keep the bounce rate under 2%. A hard bounce suppresses the address automatically; check the Suppressions page after each send.
• Spam complaints: keep them under 0.1%. Gmail and Yahoo require bulk senders to stay below 0.3%.
• Opens and clicks on the broadcast's stats. A sudden drop often means mail is going to spam.
• Google Postmaster Tools and Microsoft SNDS show how those providers rate your mail; connect them on the dashboard's Sender reputation card.

If the numbers get worse, lower the daily limit (or the warm-up target), send only to your engaged segment for a few days, and clean addresses that bounce. Broadcasts and sequences also pause on their own when their bounce or complaint rates get too high, and the Sender reputation card alerts you when Gmail or Outlook start rating your mail as spam.