Why is my new ESP blocking addresses with an invalid domain block reason when they were delivered by the previous ESP?

Email marketer from Quora responds that the new ESP may be more sensitive due to a lack of IP reputation. Even with dedicated IPs, a warmup process is required. The new ESP could be blocking more aggressively to avoid being flagged as a spam source early on.

Email marketer from LinkedIn recommends that it's possible that the domains were previously suppressed due to bounces or complaints on the previous ESP and that the new ESP has integrated with a shared suppression list. Check if the domains are on any suppression lists within the new ESP.

Email marketer from EmailGeeks Slack mentions that even with cold IPs that are being warmed up, a new ESP could be more sensitive if the IPs have no prior reputation and might block more aggressively.

Email marketer from Email Geeks raises the possibility that the previous ESP may not have actually delivered the mail and may have included suppressed recipients/domains as 'delivered' in their reporting.

Email marketer from Litmus indicates that inconsistencies between list cleaning processes may be the issue. If the new ESP has stricter list hygiene practices than the old, more addresses can be seen as invalid.

Email marketer from StackOverflow explains that different ESPs have varying levels of strictness when validating email addresses. The new ESP may have a more aggressive or up-to-date blacklist, or they may be using a different validation service that flags domains more readily.

Email marketer from Reddit shares their experience that they had a similar issue and found the DNS hadn't propagated correctly. The new ESP was using different DNS servers that were picking up the change later.

Email marketer from Email Marketing Forum suggests the best first step is to contact the support team of the new ESP. They may be able to offer specific insights into why those domains are being blocked, or if it is a technical issue with their own system. Get the ESP to review the specific logs

Email marketer from SuperOffice suggests new or very young domains might get blocked by new ESPs due to the possibility of being used in spamming. The previous ESP might not have been as thorough in screening the age and reputation of the recipient domains.

Email marketer from Email Geeks shares that the error message appears when the domain in the From address of the headers does not have an MX record.

Email marketer from Mailgun Forum had a similar issue caused by temporary DNS lookup failures. The new ESP might be configured to perform more frequent DNS checks or have a shorter timeout period, leading to these failures being detected more often. Perhaps increase the timeout if configurable.

Expert from Spam Resource explains that a new ESP is likely performing more rigorous domain reputation checks. Domains previously accepted might now be flagged because of changes to their reputation (e.g., becoming associated with spam or low engagement). The previous ESP may not have had these checks in place or may have had different thresholds.

Expert from Word to the Wise emphasizes that a new ESP might have stricter standards for list hygiene. This can lead to addresses being blocked that the previous ESP accepted, as they may have had more lenient validation or hygiene processes.

Expert from Email Geeks states they wouldn’t accept mail from a system that didn’t have a MX for their 5321.from.

Expert from Email Geeks suggests that the 'invalid domain' block reason might be a misclassification by the ESP and recommends talking to them about their practices.

Expert from Email Geeks suggests that the ESP might be having problems validating an MX record for the 5321 or 5322 domain.

Expert from Email Geeks advises against assuming the block reason 'invalid domain' directly means the recipient domain doesn't exist. He suggests investigating whether the recipient MX rejected the email with an 'invalid domain' message, or if the ESP preemptively suppressed the recipient address. He also says it could mean that the MX you reached hasn’t been configured (“paid”) to serve mail for that domain.

Documentation from AWS specifies that incorrect SPF records could be the reason for domain blocks. The new ESP might do more thorough SPF checks than the old, and incorrect configurations lead to sending failures.

Documentation from Mailjet states that a 'domain does not exist' error indicates the receiving mail server could not resolve the domain name in the recipient's email address. This is different from a mailbox not existing; the domain itself is the problem. This can be a temporary DNS issue, or the domain may genuinely be invalid. Previous ESPs may have bypassed this with retries, or older data.

Documentation from RFC 2821 explains that mail exchangers are specified by MX records in the DNS. If no MX records are found, the address is treated as if it had an implicit MX record with a preference of 0, pointing to that host. New ESP's may be validating that there are explicit MX records more strictly than previous ESP.

Documentation from Microsoft details the need to set up DomainKeys Identified Mail (DKIM) properly. This authentication method helps verify the sender's domain and is more strictly enforced now than in previous years by many inbox providers.

Documentation from SparkPost explains that an 'invalid domain' error can occur if the recipient domain's DNS records, such as MX records, are improperly configured or unreachable at the time of the connection attempt. This can happen if the domain is new, has recently changed DNS settings, or is experiencing DNS server issues. The previous ESP might have had a different retry policy or DNS caching that masked these intermittent issues.