An envelope with FREEPOST MONZO on it has been returned to me in Scotland. It has traveled to the main hub in Edinburgh, got stamped and then got back to me.
So if you like to get things done at the first attempt (or ever, in some cases), this is a bad advice “Write FREEPOST MONZO (nothing else!) on the envelope” https://monzo.com/help/payments-getting-started/cheque-how-to-pay
In my experience, providing a return address has always resulted in the letter being rejected and returned.
My best guess is that the sorting office camera’s scan the envelope, detect a full address, check for the correct postage, it fails + is rejected.
I’ve sent about 8 cheques in 2-3 years. I had one particular cheque that was high value, so of course listed a return address. It was rejected, and failed a further five (5!!) times, all with fresh evelopes before I decided to try it without the return address. It arrived safely the first time I excluded the return address.
Used this service twice for cheques and they arrived fine, I also don’t write a return address on the envelope
That sounds anxiety inducing! At that point I’d probably just pay for recorded postage to the address Monzo provide.
Well, at least some of you are definitely very brave people - to send cheques with no return address. Unfortunately I’m not so.
I think just adding the real address will be enough, like so:
Freepost Monzo
38 Finsbury Square
London
EC2A 1PX
Pretty sure I heard somewhere that if an item of Royal Mail post gets lost, it goes to the lost post centre in Belfast, and if there isn’t a return address on the outside they open it up and check if there’s a return address on the inside first before declaring it lost. So if you are concerned about it getting lost, you could instead put a slip of paper in the envelope with ‘return address’ and your address on it, and it would ultimately have the same result. Or possibly even write your name and address on the back of the cheque? I don’t think that would affect Monzo cashing it in? Pretty sure you can write anything on the back and it doesn’t matter, but could be wrong
Return address goes on the back of the envelope.
this guy has done it, the result is the same Sending cheque to Monzo
This is what I would do.
Personally, any time a “short code” freepost address has been provided to me, I have always added the full address underneath.
It’s still freepost since you write that bit first!
Guys, thank you very much for all the advice, I’m pretty sure it will get through with the real Monzo address just fine.
My point was to share the information, not to seek an advice 
That would be my suggestion. If I was sending a cheque I would have an A4 ‘letter’ sheet wrapped around it in the envelope anyway, as would be worried about a cheque on its own being seen through the envelope and pinched. So I’d have the return address on that sheet.
It does sound like it’s an automated sorting fail. As the machines don’t know which side of the envelope is the front, they’re going to identify the side with the longer address as the ‘front’ and frank that, aren’t they?
ETA:
Just realised though, what happened to you doesn’t make the above bad advice. Because you wrote something else on the envelope.
no, just for me advising anyone to send any asset without the return address IS a bad advice
Yeah I know that was your point.
I’m just posting to agree, so hopefully others will see and follow that advice.
I wonder if Monzo themselves have ever sent any cheque with no return address 
Another option is to send it tracked. Details are within the ‘paying in a cheque’ help article:
Monzo desperately need cheque imaging… I had to post a high value cheque a couple of months back and sent it to Monzo tracked. But that cost me money. Which is annoying. The irony is that most ‘legacy banks’ are less legacy and have already implemented cheque imaging…
yeah, which was implemented in the US like decades ago… can’t be that difficult then, can it?
“Freepost Name”, like Freepost Monzo, is valid, but from your picture it looks like you put a return address on the front? The mail centre machines try to locate a full address on the front of the envelope, so if they find one then they’ll sort it straight back to you. Return address goes on the back.
(at one time I led the team that provides the software to do Royal Mail’s letters sortation)
They do know which is the front, but they’re trying to do something called address block location (ABL) to pick the area that looks most like an address, before then using OCR and other techniques to figure out where to sort it to. In this case the ABL picks up the return address as being more likely to be the destination than just Freepost Monzo.
Might sound a strange choice, but if you think how busy junkmail or magazines can be, ABL is quite a hard problem and it occasionally goes wrong. Generally it then goes for manual keying, but on this occasion i’m guessing it believed it had a full-depth sort.
Royal Mail have a good guide for how to put a return address:
Write the words ‘return address’ on the back of the envelope and underneath that, the actual return address.
so here’s the man we all have to “thank” for our returning letters (just kidding)
as i said before, the letters with the return address on the back would return to you just as well Sending cheque to Monzo
It’s a harder problem than it might seem - we get very close to 100% right for on-spec machine print (like your bank statements) but junkmail, handwritten letters (especially christmas cards), and polywrap magazines and catalogues are hard. Throughput’s high too, each machine will do more than ten letters a second, and we have to OCR all of them in real time. Of course, we only notice the ones that go a bit wrong 
