Instantly Email Warmup: How It Works and How Long to Warm Up Inboxes
What email warmup does, how to use Instantly warmup sensibly, and why warmup alone does not guarantee inbox placement.
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Email warmup gradually builds a positive sending history for a new or inactive inbox before you use it for cold outreach. Instantly’s warmup does this by sending emails between your inbox and other accounts in its warmup network, which open, reply to and rescue those emails from spam where needed. This tells mailbox providers the inbox is behaving like a normal, trusted sender. Most practitioners warm new inboxes for at least two to three weeks before sending campaigns, and keep warmup running afterwards.
Why new inboxes need warming
A brand new domain and mailbox that suddenly sends dozens of emails to strangers looks exactly like spam behaviour. Mailbox providers such as Google and Microsoft judge senders partly on history and engagement. Warmup creates a track record of normal sending and positive engagement, so your first real campaign does not arrive from an account with no reputation at all.
How Instantly warmup works
Once you enable warmup on a connected account, Instantly gradually increases the number of warmup emails it sends and receives, according to your settings. Those emails are opened and replied to by other accounts, and moved out of spam folders if they land there. Warmup emails are typically tagged so they can be filtered and do not clutter your inbox.
Recommended approach
- Warm before you send: give new inboxes at least two to three weeks, longer for brand new domains.
- Ramp up gradually: start with low daily warmup volume and increase slowly.
- Keep warmup on during campaigns: it helps maintain reputation as you send real outreach.
- Keep campaign volume modest per inbox: spread volume across more inboxes rather than pushing one hard.
- Monitor health scores: watch the warmup and deliverability indicators Instantly provides.
Warmup cannot fix everything
Warmup helps reputation but does not override other problems. These will still hurt deliverability:
- Missing or incorrect SPF, DKIM and DMARC records.
- High bounce rates from unverified lists.
- Spam complaints from poorly targeted recipients.
- Sending too much too fast from each inbox.
- Spammy content, heavy links, images or tracking.
- Sending cold email from your main business domain.
Our guide to cold email deliverability covers all of these.
Signs your reputation is slipping
- Warmup emails increasingly landing in spam.
- Falling reply rates without changes in copy or targeting.
- Rising bounce rates.
- Inbox placement tests showing spam or promotions placement.
If you see these, reduce sending, pause the affected inbox if necessary, check DNS records and list quality, and let warmup continue before resuming.
Warming old or existing inboxes
An inbox that has been used for normal email for years has history, but suddenly adding cold outreach is still a change in behaviour. If you must use an existing inbox, which we do not recommend for your main domain, start very slowly with warmup enabled. For anything beyond light outreach, separate domains are safer. See our Instantly setup guide.
Get your sending infrastructure right
We set up domains, authentication, warmup and sending limits so your campaigns start with a healthy reputation and stay that way. See our AI Automation Systems service or get in touch.