Does email warmup actually work? Most answers online are opinions. Here is data. Five real senders from the Mailwarm network, anonymized, measured week after week.
Short answer: yes, when it runs long enough and your authentication is right. It is not instant, and it is not magic. Here is what it looks like in practice.
First, what we measured. Spam rate is the share of a sender's emails that land in spam, across the inboxes Mailwarm monitors. We compare the first test with the average of the last four weeks, with Gmail, Outlook and the other providers pooled.
Sender A started at 75.6% in spam. Three emails out of four never reached the inbox. Fourteen weeks later, the spam rate averaged 11%. And volume grew at the same time, from 250 emails to more than 4,000.
Sender B went from 63% to 12%, in 21 weeks. Sender C, from 44 to 11%, in five weeks. Sender D, from 42 to 3%, in just two weeks. And sender E, from 38 to 7%, in seven weeks.
Two patterns stand out. One. Volume went up while spam went down. Reputation grew with activity, instead of breaking under it. Two. Timing varies a lot, from two weeks to twenty-one. Domain age, sending history and authentication all change the timeline.
To be clear, these are among the strongest recoveries we measured. They are not averages. And warmup was one part of what these senders did, alongside fixing authentication and sending habits.
If you want results like these, do four things. Fix SPF, DKIM and DMARC first. Start warmup before your first campaign. Ramp up slowly. And keep a maintenance level running after.
Mailwarm is an email warmup and deliverability monitoring tool, built by a Y Combinator team since 2020. It is built to be the best email warmup tool for teams that depend on the inbox: real inbox engagement, live inbox and spam tracking, and a deliverability expert in every plan.
Not sure where you stand today? Run the free email deliverability test on mailwarm.com. The link is in the description.
