Invalid TLD in MX Record

[SDATTJack]

We are BT Business Email users which has recently been upgraded to Office 365.

Some of our users are receiving undelivered email notifications which declare the message has not been delivered because of security policies, with the error message:

Sender address rejected: "invalid" TLD in MX record # #

Any help or suggestions would be much appreciated.

[minalo1]

Try following 

You can try adding .mail.eo.outlook.com after invalid

MX  @   xxxxxxxxx02.msv1.invalid

MX  @   xxxxxxxxx02.msv1.invalid.mail.eo.outlook.com

The other is to delete MX record, but never done the delete and not recommend, as with all take a snapshot or save to before any alteration

[Caplet]

Hi minalo1.... I am having the sam problem as the original poster, but your reply makes little sense to the uninitiated (I am just looking up what an 'MX' record is)

Who needs to edit the MX record? us the sender or the intended recipient?

If it is us the sender... where do I edit the MX records? we have our domain hosting with BT, can I edit the MX records through them? and if so do you know how?

Thanks in advance

[sterobbins]

I am also getting this when sending to a user at demon.co.uk. His IT guy says my MX records have prefixes of 1, 10 and 50, and it's the 50 that's invalid.

I also don't know what an MX record is or what to do about correcting this.

[sterobbins]

I went onto the chat line and they have fixed my problem! Suggest you others do the same.

[furriephillips]

This problem occurs because the sender's domain has a bogus MX record.

The reasoning behind why an MTA might not accept a mail from a domain whose MX records contain an invalid entry, is that there is a duty of care once you accept an email onto your system. You need to be able to send bounce messages in case of non-delivery, but if the sender domain's MX records are invalid, you can't ensure this ability, so rejecting the mail is the most prudent option.

The invalid MX record has most likely been introduced, because someone has added a new (and bogus) MX record to the domain, in order to prove domain ownership during the Microsoft Office365 migration process.

Although there is the option to add a "TXT" record (which should not adversely affect any services), it appears that many people are adding bogus "MX" records instead (which is likely to cause problems with mail delivery). Either way, once the domain ownership verification process has been completed, the temporary DNS records should be removed (especially if it's a bogus/invalid MX record).

You can view a report on your DNS setup (including MX record validity), using this tool. Here is an example excerpt from a DNS report of an Office365 customer, who has not removed the temporary MX record: -