- IP reputations can be a good indicator of trustworthiness to mailbox providers for senders that have dedicated IPs with a long sending history and have relatively good sending metrics.
- IP reputations are used by all major mailbox providers as one of their indicators. This makes having a good IP reputation, as represented by Return Path's SenderScore, a good idea.
- An IP address may be shared among many senders, which is common when sending from an Email Service Provider (ESP). If a good sender and bad sender share the same IP address, the good sender can be penalized by the bad sender's poor sending practices.
- Spammers change IPs often in an attempt to circumvent IP reputation filters. Because spammers frequently send from new IPs, mailbox providers' spam filters scrutinize all new IPs. As a result, senders that use new IPs need to go through a sometimes lengthy warm up process which can be disruptive to their business if not managed properly.
- Generally, domains are more reliable than IPs for verifying your identity.
- Domain reputation helps mailbox providers to collect and store reputation metrics about senders on shared IPs. Some mailbox providers, such as Microsoft, put more weight on domain reputation for senders using shared IPs in order to reward good senders and identify bad senders.
- Domain reputation is becoming more reliable and important to mailbox providers due to spammers frequently changing IPs and the increased complexity and sophistication of email marketing programs.
- It is easier for mailbox providers to filter spam using domains when senders use IPv6, which is a new way to assign an IP address to your computer device. IPv6 IP addresses number in the trillions, so trying to reliably measure reputation metrics from these IPs is very difficult.
- A domain with a good sending reputation can speed up the process of warming up new IP addresses.
- Domains are easily spoofed in phishing messages which tricks the recipient into thinking the email came from your brand. When a spammer spoofs a domain, the bad metrics from the spam messages can unfairly penalize the owner of that domain. Domain spoofing is why implementing DMARC is an important part of your email marketing strategy.
- Senders may share domains between corporate and marketing email. If sending best practices are not followed for marketing email, it can result in a poor sending reputation which may cause corporate email to be filtered or blocked by some mailbox providers.