Every new domain or subdomain used for email starts with a slightly negative reputation due to the high volume of spam-related domains created daily. Until we establish a strong sender reputation, there is a significant risk of deliverability issues. To mitigate this, we must start gradually, allowing email algorithms to recognize us as a reputable sender.

Email providers and ISPs use automated anti-spam systems that reward consistency and controlled growth. In general, the slower we scale our email volume, the better our chances of maintaining strong inbox placement. However, business needs may sometimes require faster ramp-ups, which increase the risk of emails being filtered to spam, blocked, or even blacklisted.

The following best practices are guidelines, not strict rules. There may be times when we need to send more emails at a faster pace, but doing so comes with additional risks. Whether that risk is acceptable is ultimately a business decision. While iPost can assist with deliverability issues if they arise, the best approach is to proactively prevent problems through careful volume management.

Daily Mail Volume: Guidelines

If possible, mail at each volume level for 3-4 mailing days:

  1. Start low. 1,000 emails per day is standard, but 500 is better for a mailing list with issues. If the list is squeaky clean and engagement is high, starting at 5,000 per day is a reasonable risk.
  2. As long as the daily volume is below 50,000, doubling when increasing is normally safe.
  3. When daily volume is at or above 50k and still below 100k, increases of up to 50% are a reasonable risk.
  4. Once the daily volume is above 100k, increases of up to 20% are a reasonable risk.
  5. If our daily volume goes above 250k, increasing by no more than 10% after that is the safest strategy.

Keys to Warmup Success:

  1. At the start and for as long as possible, send to the most engaged recipients--for example: those who have opened or clicked in the past 30 days.
  2. Do NOT manually select which IP to send mailings on. The system automatically balances the load over the assigned IPs.
  3. Do NOT manually set sending speed unless iPost has instructed us to do so. The system default is optimized to maximize delivery and minimize risk.
  4. Monitor the metrics and adjust the plan in case of problems--i.e. back off mail volume, send less promotional content, or mail only to engaged recipients.

What to Expect:

  1. At first, a large percentage of soft bounces from the large ISPs (especially Yahoo/AOL). This will gradually subside.
  2. If the delays continue longer or build up a backlog of undelivered mail, we might need to back off the volume of mail for a few days.
  3. For at least 2-4 weeks, some percentage of mail junked at the large ISPs. Positive engagement metrics help clear this hurdle faster.
  4. Blocking by some domains if the list has low engagement. iPost will apply for unblocking, but this is a signal that we need to improve engagement.

After the Warmup is Finished:

  • Never increase mail by more than 20% over the previous week's average daily total (10% if we're above 250k per mailing).
  • Monitor metrics and in case of issues, back off the total daily volume.