Why are we getting DNS resolution failures with outlook.com when sending email?

Email marketer from Mailjet shares that deliverability problems with Outlook are often traced to domain reputation and email authentication (SPF, DKIM, DMARC) problems. Ensure that your sending domain has a good reputation with Microsoft and that your emails are properly authenticated.

Email marketer from MXToolbox explains that if your sending IP or domain is blacklisted by a DNS-based blacklist (DNSBL), outlook.com may refuse to accept connections, leading to DNS resolution failures. Check your IP and domain against common blacklists.

Email marketer from Email Geeks explains that a single PowerMTA config change to add the following line... ```edns-udp-length 2048``` Since adding it, the problem has not occurred again where it was.

Email marketer from Neil Patel shares that DNS resolution failures may stem from incorrect DNS settings, such as misconfigured MX records or DNS propagation delays, which can prevent email servers from locating the correct destination server for outlook.com.

Email marketer from Reddit suggests that outlook.com might be greylisting your emails due to a new or low-reputation IP address. This results in temporary DNS resolution failures as part of their spam filtering techniques, where initial attempts to deliver are deferred.

Email marketer from EmailOnAcid explains that a poor IP reputation can lead to email delivery problems with outlook.com. Microsoft may block or delay emails from IPs with a history of sending spam, leading to DNS-related errors during the connection process.

Email marketer from DigitalOcean explains that the lack of a proper Reverse DNS (PTR) record for your sending IP address can cause email servers, like those used by outlook.com, to reject connections, leading to DNS resolution failures. Ensure a PTR record is configured that matches your sending domain.

Email marketer from Gmass suggests email warming has not been correctly implementted on your IP/Domain. Sending too many emails too quickly after setting up your new Domain or IP

Email marketer from Google Groups shares that if your server is attempting to connect to outlook.com using IPv6, but there are IPv6 connectivity issues, this can lead to DNS resolution failures. Ensure IPv6 is properly configured, or try forcing IPv4.

Email marketer from SuperUser forum shares that MTU (Maximum Transmission Unit) size issues can cause DNS resolution failures. If packets are too large, they might be dropped, leading to resolution problems. Adjusting the MTU size can sometimes resolve this issue.

Email marketer from StackOverflow responds by suggesting that DNS caching issues on your sending server or network can cause intermittent resolution failures. Flushing the DNS cache or using a different DNS server may resolve the problem.

Expert from Email Geeks, supported by Email marketer Danial Thorpe, explains that there is something weird with what microsoft are returning for that hostname - and it’s varying at random - though it’d take some digging to see just what. But if there’s something in your DNS resolution chain that barfs on >512 byte responses (which isn’t an unusual thing) that’d explain it.

Expert from Email Geeks, supported by Email marketer Danial Thorpe, explains that the issue is caused by three separate problems: Microsoft's authoritative DNS sometimes returns inconsistent records, DNS resolution truncates large responses, and the truncated answer isn’t handled properly by local resolver.

Expert from Word to the Wise responds by emphasizing that incomplete or incorrect email authentication (SPF, DKIM, DMARC) setup can lead to DNS resolution-related issues. Outlook.com might require proper authentication to verify the sender's legitimacy; failing this, it may result in DNS resolution failures or connection refusals.

Expert from Spam Resource explains that DNS resolution failures can occur if the sending IP address or domain is listed on one or more DNS-based blacklists (DNSBLs). Outlook.com may reject connections from blacklisted sources, leading to these failures as part of their spam filtering measures.

Expert from Email Geeks explains that the "unable to route" error suggests a problem with the recipient domain or local DNS servers, rather than the sender's DNS configuration, especially regarding resolving DNS queries with large results.

Expert from Email Geeks explains that the second (bad) DNS response is often truncated (TC bit is set), which means the resolver should retry via TCP, and the truncated answer isn’t handled properly by the MTA DNS handling code.

Documentation from Microsoft Support explains that transient DNS lookup failures can occur due to network connectivity issues or DNS server unavailability, and recommends implementing retry logic in the email sending application to handle such temporary failures.

Documentation from AWS Documentation explains that Route 53 DNS resolution failures can occur if the DNS records for outlook.com are not properly configured or if there are issues with the AWS DNS servers themselves, leading to temporary or persistent failures.

Documentation from DNSViz explains that if DNSSEC is enabled on your domain or outlook.com's domain, validation failures can lead to resolution problems. These issues often arise from misconfigured DNSSEC records or problems with the chain of trust.

Documentation from PowerMTA explains that incorrect DNS timeout configurations in PowerMTA can lead to resolution failures. Adjusting the timeout settings to allow more time for DNS lookups may resolve the issue.

Documentation from RFC Editor explains that DNS has inherent limitations, such as UDP packet size limits, which can cause truncation and subsequent failures if DNS responses are too large. This can be especially problematic if outlook.com's DNS records are extensive.