IP Warm-up: The Path of the Good Sender

opinionThe following is a guest contributed post from William Astout, Email Marketing Expert and L2 Deliverability Consultant at SmartFocus.

An IP warm-up plan is vital for any high-volume sender moving to a new IP address or addresses. Even though there is no silver bullet for warming up IPs, there are some practical guidelines that senders can follow to adequately warm-up their sending IPs without causing any issues with Internet Service Providers (ISP).

The purpose of a warm-up plan is to introduce a new sender to ISPs’ spam filters, demonstrating the emails sent from that IP or IPs are legitimate. The majority of mail from an unknown IP is treated as spam, and with the warm-up you’re gaining the trust of spam filters so they won’t treat legitimate emails as spam. So, during a warm-up plan it is imperative that clients focus on their absolute best and most active data, which is most likely to generate the best engagement rates.

Sender Reputation

The way ISPs separate good from bad senders is by looking at the sender’s engagement rates, in addition to several other measures.

ISPs assign reputation scores to both sending IPs and sending domains:

  • IP reputation is based on messages received from an IP (or range of IPs) and is enforced at the IP level of anyone using that IP
  • Domain reputation is based on messages received from a domain and delivery policies are based on that domain rather than just IP

It is much harder to improve a bad reputation than to start-off correctly, even at slower rates initially.  Because of that, we advise clients to adhere to the guidelines set out in our bespoke warm-up plans.

Getting Started

The pace of a warm- up plan will depend entirely on the quality of the client’s database, and there are limitations to how much mail volume can be sent out.

Co-registered lists should be avoided at all costs. These people didn’t opt-in to receive mail specifically and will complain. Using purchased, or rented lists contravene anti-spam policies and will result in poor results, affecting the good, opted-in data.

As previously stated, it’s imperative that senders focus on their best data, preferably their most recent opt-ins and most active data.  Every user opening or clicking an email will help build a positive sender reputation for the client. Every user unsubscribing, marking the email as spam, or even just ignoring it, will generate bad reputation for the sender.


Don’t be afraid of starting small, in fact, that’s the very point of a warm-up plan. Some ISPs i.e. AOL may bounce emails sent by the hundreds, so start with a few dozens, and closely monitor the progress to see if emails continue to be accepted as you send them. Send only a few hundred in the first few days, and increase the volume to a few thousand per ISP by day 3 or so, depending on the success of the first sends.

The first week shouldn’t see a sending volume higher than 15k emails per day, per ISP. These are guidelines only, and intended for the larger receivers. I would not try and push 15K to the likes of BT internet from day 1 or smaller providers, and definitely not QQ.com. By the second week of sending, if all is well, senders can double their volume. By week three they can send three-times as much, and so on until they reach their desired sending volume.

It’s also important to keep the volumes consistent to whatever sending patter is required. If emails are meant to be sent on a weekly basis, keep the warmup consistent to that.


Now you’ve sent your campaign, track the activity. The sender should keep tracking their rates and metrics over time. Are things trending up or down?  Is something significantly different than the standard benchmark? If their results are good, they’ve got a good sender reputation.

However, if that’s not the case, it’s important to identify the troublesome domains (easily obtained through ISP reports), cut-back to acceptable volumes and re-try a more modest volume increase than what it was attempted previously.

At this point there should be virtually no hardbounces, complaints or unjoins. This is the point of taking the best possible data, so the sender can build a good reputation with ISPs in a short period of time.

If senders follow these instructions, they will minimise potential problems with receiving domains.