What factors influence how many IP addresses I need for my email marketing program?

Determining how many IP addresses your email marketing program needs can be difficult. Whether or not you need one or more IP addresses depends on your email marketing program objectives.

Common scenarios

  • A small or mid-sized business that sends a weekly promotional newsletter likely needs only one IP address.
  • A mid-sized business that sends promotional emails twice per week and sends receipts and shipping notifications to the U.S. and Europe may need up to two IP addresses for each region--one for marketing messages and one for transactional messages--for a total of four IP addresses.
  • Large businesses with more than one brand that send worldwide may need multiple IP addresses based on the number of brands they have, the regions they mail to, and the email streams or types that they send.

Each business must assess its own objectives. There may also be some limitations to consider:

  • You may only have the budget for one IP address.
  • If you use an email service provider, you may be limited to one IP address for transactional emails and one for marketing emails.

Check with your email service provider about limitations or policies they have regarding the use of more than one IP address. Your email service provider may also be able to provide guidance for what might work best for your business.

When assessing the number of IP addresses you need, there are many factors to consider.

The number of email streams or email types
Most senders start simply and categorize their emails as either:

  • Marketing
  • Transactional or triggered

In this case, one or two IP addresses per email stream will usually suffice.  

Larger, more sophisticated senders may have more email streams or types to consider. For example, email streams may need to separately address:

  • Promotional or marketing messages
  • Transactional messages
  • Triggerred messages

Email types may include:

  • Newsletters
  • Welcome messages
  • Win-back messages
  • Product updates
  • Receipts
  • Order confirmations
  • Birthday or anniversary messages
  • Thank you messages

The number of brands
Many mid- to large-size businesses have multiple brands handled by the same marketing department. For tracking and reporting purposes, many senders with multiple brands allocate one or more separate IP addresses for each brand. If brands only send email periodically or at low volumes, then separate IP addresses for each brand may not be necessary.

Risk to reputation
Separate IP addresses may be appropriate if a new campaign may place a solid, well-established sending reputation at risk. By launching a new campaign from a separate IP address, you can isolate and gauge reaction to it by monitoring metrics including:

  • Inbox placement rates
  • Sender Scores
  • Smart Network Data Services (SNDS) data
  • Complaint rates
  • Unknown user rates
  • Spam trap hits
  • Bounce log data
  • Certification reports

Separate IP addresses may also be appropriate if a change in list acquisition practices may place your established sender reputation at risk. For example:

  • Email deliverability rates for all of your campaigns may suffer if you deploy invite-my-friend emails (a known, high-risk list acquisition technique) from an IP address with a good reputation.
  • As noted in our 2012 Sender Score Benchmark Report, social networking senders have the highest frequency of spam trap hits because they often use the import-address-book method to grow their list file.

Sending volume
You should also consider the volume of email you plan to send to determine if you need extra IP addresses. Unfortunately, there is no hard and fast correlation of IP addresses to sending volume. One sender may able to send a higher volume per IP address because of its positive sending reputation, while another sender may be limited because of its high levels of unknown users and spam trap hits.

Time-sensitive delivery
You may need additional IP addresses if you need to get out a large volume of emails in a short period of time (for example, if you offer flash sale promotions that are valid for only a few hours). To help calculate your needs:

  • Check for posted hourly rates: Check the postmaster sites of mailbox providers to determine if they post their hourly rate limit. Comcast can receive up to 86,400 emails per hour when the IP address Sender Score is between 86 to 100. If you have 3 million Comcast subscribers and need to get your email out within an hour, then you'll need 4 IP addresses.
  • Check your SMTP log files: Not all mailbox providers post their hourly rates. In that case, use your log file data to determine your actual hourly rates by mailbox provider. For example, if your logs show that you can send 2 million emails to (Hotmail) within an hour and you need to send 10 million emails within an hour, then you need 5 IP addresses.

More isn't always better
Sending email from a large number of IP addresses should be reserved for large, sophisticated senders. There is no rule that specifies how many IP addresses to use. However, a good guideline is to keep the number of IP addresses to a minimum. Many spammers use a large number of IP addresses in an attempt to avoid spam filters, so sending from a large number of IP addresses may cause deliverability problems.

Related resources
Return Path Blog: 4 Factors For Deciding How many IP Addresses Your Email Marketing Program Needs

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