Mail delivery failed: returning message to sender

[#1]

I'm getting this reply from an email address I've been using happily for the last year or more, and from which I had an incoming message about a week ago (I have replaced the actual address with X's):

A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server 74.125.24.26 responded with: **XXXXXX@XXXXXX.XX.XX 550:5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 l4si20857725wie.68 - gsmtp This message was created automatically by mail delivery software on the server avasout04.

The target address is not a gmail address, it was not sent from a gmail addess, so why am I seeing a link to a google site, and why is the remote server 74.125.24.26 also apparently a google one?
I have successfully pinged the target domain.
Can anybody throw any light on this?

[#2]

Without knowing the destination address it's hard to ascertain what's happening.

Quote from: kbturner

The target address is not a gmail address, it was not sent from a gmail addess, so why am I seeing a link to a google site, and why is the remote server 74.125.24.26 also apparently a google one?

It may not be a GMail address but that doesn't mean the domain isn't still hosted with Google. Regardless, it's not an SMTP rejection our servers would return so whatever the problem is, it almost certainly lies at the recipient's side.
If I had to guess, I'd say that the recipient is trying to move their domain/email hosting to Google and has messed something up in the process.

[#3]

Quote from: Bob

Without knowing the destination address it's hard to ascertain what's happening.

The destination address is kenton.ac.ke, and a whois search responds as I would expect it to, with no mention of google.

[#4]

adw@nofate:~$ dig kenton.ac.ke mx
; <<>> DiG 9.9.5-8-Debian <<>> kenton.ac.ke mx
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56617
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;kenton.ac.ke.                  IN      MX
;; ANSWER SECTION:
kenton.ac.ke.           300     IN      MX      10 ASPMX2.GOOGLEMAIL.COM.
kenton.ac.ke.           300     IN      MX      10 ASPMX3.GOOGLEMAIL.COM.
kenton.ac.ke.           300     IN      MX      50 mail.kenton.ac.ke.
kenton.ac.ke.           300     IN      MX      100 mail.jtl.co.ke.
kenton.ac.ke.           300     IN      MX      1 ASPMX.L.GOOGLE.COM.
kenton.ac.ke.           300     IN      MX      5 ALT1.ASPMX.L.GOOGLE.COM.
kenton.ac.ke.           300     IN      MX      5 ALT2.ASPMX.L.GOOGLE.COM.

An MX lookup however does show the domain is using google as it's SMTP servers.

[#5]

Yep, and whilst I can't check without knowing the full email address (which I'd suggest against posting here), I've a suspicion that these servers will accept and deliver email for the domain:

50 mail.kenton.ac.ke.
100 mail.jtl.co.ke.

Whereas these will result in the SMTP rejection you're seeing:

5 ALT1.ASPMX.L.GOOGLE.COM.
5 ALT2.ASPMX.L.GOOGLE.COM.
10 ASPMX2.GOOGLEMAIL.COM.
10 ASPMX3.GOOGLEMAIL.COM.

Probably because things aren't set up correctly at Google's side to accept mail for the domain.

[#6]

Hmm, that's interesting, avatastic.  Maybe, as Bob Pullen suggested, they're in the middle of moving their hosting to google.
By the way, my correspondent, quite independently, also has a GMail address, and I'm getting similar undeliverable responses when I use that address.
Just seen your second response, Bob.  I'll PM you shortly with more details.