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net: LookupMX does not consider IP addresses as valid records #56025
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By the way we ran into similar issue: the |
I've noticed this a bit, lately. Here's a handful of domains with MX records where at least one is an IP address (as of 2024-04-19):
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CC @rolandshoemaker @golang/security |
We currently support domain names that contain digits in arbitrary places, but it also has to contain at least one non-digit character (except dots). Line 22 in 903e0ff
Also RFC 1123:
RFC 8499:
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RFC is great, but we are talking about the real world. And the reality is that people do not read RFC. Being a bulk email sender (mailgun.com) we stumbled up on such cases. Currently we are getting around by using private |
@horkhe could you provide some data on the rates at which you see this issue? I am not particularly opposed to being more lax here (i.e. just loosening the restriction to LDH+IP), but I don't want to do this if we're only fixing a very small number of otherwise incorrectly behaving servers. If there is data that shows this is actually significantly common, and there are high-volume mail servers that are relying on this behavior, then it would perhaps be reasonable to do. |
@rolandshoemaker sorry I missed this question. We at Mailgun deliver about 20_000 emails to MX hosts configured with IP addresses per day. |
Change https://go.dev/cl/651056 mentions this issue: |
This is a followup to #46979. I found another case where https://golang.org/cl/322230 broke the original logic. Even though MX records MUST contain domain names, occasionally they contain IP addresses. And this change considers IP addresses as invalid records and returns an error making delivery to respective email service providers impossible. The number of such cases is minuscule in the great schema things, but still we at Mailgun handle a few thousand messages to such email providers per hour. So in the spirit of Robustness Principal I believe a change should be made to allow IP addresses in MX records.
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