Receiving servers judge an unknown sender by behaviour. A domain that has never sent anything and suddenly sends thousands is the precise signature of a compromised account, and it is filtered accordingly. Warming means starting small and growing, so there is a history by the time volume matters.
Before sending anything
- SPF, DKIM and DMARC in place and passing - see SPF, DKIM and DMARC.
- Reverse DNS matching the sending hostname - see reverse DNS for a mail server.
- A working unsubscribe, and a list you actually have consent for.
A schedule that works
week 1 50 a day
week 2 200 a day
week 3 500 a day
week 4 2000 a day
then roughly double weekly while complaints stay lowSend to your best addresses first
Start with the people most likely to open and reply - recent customers, active accounts. Early engagement is what builds reputation. Starting with a three-year-old list does the opposite, and dead addresses bounce, which is the worst possible first impression.
Never begin by importing an old list. Bounces and complaints in the first week can end a domain's reputation before it has one, and recovering is far slower than warming would have been.
Watch the numbers, and slow down if they move
- Bounce rate - under 2%. Above 5%, stop and clean the list.
- Complaint rate - under 0.1%. Above 0.3% is serious.
- Open rate - a proxy for whether you are in the inbox at all.
Read the DMARC reports
v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.comThey arrive daily and show who is sending as your domain and whether it passes. During warming they are the fastest way to find a misconfigured sender you had forgotten about.
If you are moving from an old domain, keep sending some volume from it during the transition rather than stopping dead. A sharp move of all traffic to a new domain is warming with no ramp.