Do you need to warm up a mailbox for cold email?

Two things get called warm-up, and they are different. The first is ramping up volume slowly on a mailbox that has no history. The second is paying a service to exchange automated messages between mailboxes. The first is sound practice. The second is optional, and the evidence for it is thinner.

What is certain about a new mailbox?

A new mailbox has no reputation. Mailbox providers learn how a sender behaves from its history: bounces and complaints. A sender that appears and sends 200 emails on day one gives them nothing to judge it by and a sharp rise to react to.

Three things are within your control, and none needs a service.

• A gradual volume. Start with a low daily limit and raise it in small steps.
• Authenticated DNS. SPF, DKIM and DMARC records should pass before the first message. Gmail and Yahoo expect them from bulk senders, and they are sensible for any sender.
• A clean list. Hard bounces from unverified addresses damage a young sender faster than anything else, so verify the list before you send.

What do warm-up services do?

A warm-up service connects your mailbox to a pool of other mailboxes. They send each other messages, open them, reply and pull them out of spam folders. The aim is to build a pattern of positive activity before you send real campaigns.

The claim that this improves inbox placement comes mainly from the vendors that sell it. We know of no independent measurement that we can cite. Mailbox providers are aware of the technique and can detect artificial patterns, and a pool of mailboxes that only talk to each other is a recognisable pattern in itself. For that reason we treat warm-up as an optional extra, and we do not sell it as a requirement.

How can you ramp up by hand?

Use real sends to real prospects, with a low limit that rises in steps. The table is an example schedule.

Pause the ramp on any sudden rise in bounces. Fix the list, and do not push through it. When a limit feels safe, hold it for a few weeks before raising it again.

Does it matter how old the domain is?

Domain age is a signal, and it is not the only one. A freshly registered domain has no history at all, and some providers treat very new domains with more caution. That is a reason to register the sending domain well before the first campaign, and to avoid sending from a domain bought this week. anymail shows domain age in the mailbox domain check-up when the registry answers.

An old domain does not remove the need to ramp. A domain that never sent cold email has no cold email history, and a sudden burst from it still looks like a burst.

When might a warm-up service help?

A service can make sense when you cannot wait for a manual ramp, or when a mailbox has been idle for months and you want it active again before a campaign. Judge it by your own bounce and complaint figures rather than by the vendor's dashboard. If you try one, change one variable at a time so that you can tell what moved the numbers.

A service cannot fix a poor list or missing DNS records. It also cannot protect a mailbox from complaints that real recipients file against real emails.

What are the limits of this advice?

The ramp schedule is practitioner convention. Providers do not publish their filtering rules, so nobody outside them can state exactly what helps. Your own data is the test: if bounces stay low and replies arrive at a steady rate as volume rises, the ramp is working.

How does anymail handle warm-up?

anymail offers warm-up only through a partner, as an add-on, and it does not run its own pool. Alongside that, each mailbox keeps a daily limit you can raise by hand, a campaign pauses itself when bounces climb, and verification runs on import. The deliverability page lists what is and is not included.