Base64 encoded MX records in TXT records

A lot of domains hosted by Namecheap contain strange DNS TXT records that appear to be base64 encoded, that when decoded look like a weird kind of MX record - having the structure of both a priority and then a domain. What are these for? There does not appear to be any documentation anywhere regarding these. There are tens of thousands of examples of these, yet there is no clear purpose or documentation. Does anyone know what these are used for?

Some examples:

• everythingforsight.org. has a TXT record of MAltYWlsLmV2ZXJ5dGhpbmdmb3JzaWdodC5vcmcuCg== which decodes to 0 mail.everythingforsight.org.
• 1eyeworks.com. has a TXT record of MAltYWlsLjFleWV3b3Jrcy5jb20uCg== which decodes to 0 mail.1eyeworks.com.

My guess is this:

NOTE 1:In case you do not want to interrupt the functionality of current email services before the creation of mailboxes with us we have an alternative verification method that implies a TXT record adding on the side of the DNS provider. To get a value of a TXT record that needs to be added, please contact our Support Team.

You need to ask the owner of those zones as they are theoretically responsible for the content, not the DNS provider.

It may be for some sort of "authentication" as TXT records are often (ab)used for that, or just some bad tool. Or loose attempts at some sort of zone integrity checks.

Anyway, they don't "match". everythingforsight.org. has currently 3 MX records, none of them using mail.everythingforsight.org. as mail exchanger.

In fact, instead of asking Namecheap you should ask the company behind web-hosting.com as this is the base of the email exchangers used in the 2 domains you gave as example. Hum.... web-hosting.com seems to be Namecheap anyway too :-)