My husband received something very strange in the post ...

Do you know anyone due to get married? Perhaps he's been asked to do a reading.

How on earth can you tell it's a woman's handwriting

What do you mean - it’s a woman’s handwriting ??

Occam’s Razor - the simplest explanation is the most likely to be correct.

If he’s not actually cheated, he’s confided in someone about your marriage (and not in a positive way)

His mother? Does she think you have problems? Sorry you are going through this OP, I would do some digging now he is at work before he knows, see if you can find anything else.

I wouldn't open a hand written letter.
There's no way you can tell the sex of a writer.
Why don't you phone him and ask ?
I'd be suspicious seems odd.

Strange

Could be a letter from Jehovah Witnesses we got one last week about the meek possessing the earth.

They seem to be sending letters to random addresses as my mum received one a couple of months ago addressed to her my dad (dad had died a month earlier)

How odd. But what a skill to be able to gender hand writing. Hats off to you on that.

I wouldn’t conclude that he’s cheated from that.

It's weird, but likely only your DH knows the answer to that one.
Also, how can you tell it's a womens handwriting, unless they've written "I am a women" on there?

Message him!

Yes, it could very well be JW.

I would think- that’s weird, will be interested to hear what that’s all about later and move on. It wouldn’t occur to me that this would be some bizarre cryptic statement announcing an affair.
I’m afraid the fact you jumped to cheating as the explanation makes me think there’s more going on. Have there been other clues?

Sorry OP but unless it's a very weird kind of joke, I would also suspect cheating.
Have you noticed anything strange in his behavior lately? Or is this coming out of the blue? If you want to start looking for evidence, I would do it now, before he comes home. I genuinely hope that I'm wrong here but this doesn't look good.

Have you asked him?

My first thought was a culty church or JW.

We used to live down the road from a Brethren church and some of those people were intense.

Lots of people round here had hand written personally addressed letters like this, I believe it was JW.

If you’re so open with each other that you’re invading his privacy by opening his post then just ask him, either via text, call or wait till he gets home.

And you have no idea it’s a woman’s handwriting.

Yes my guess is Jehovah Witnesses. We received something similar in the post and it was handwritten.

Seems odd to jump to cheating as a conclusion with no other context, is there anything else going on?

I second (third?) the JW explanation.