delayed emails

My DiL has mentioned a few times recently that she is having trouble getting emails through to me. Some of them simply don't reach me, while others are delayed by anything up to two days. Also, she's had to ask me to re-send some emails to her because they haven't downloaded (if that's what emails do!) properly. For example, she has had one or two that show no content. She isn't aware of any problems sending or receiving emails from other people so assumes that the problem is at my end. However, I'm not aware of such problems with other people either - having just had a quick look through emails that I've recently received, I can't see any others that have taken long to reach me.

Earlier today, I mentioned the problem to my dad, and he immediately told me that he too has received emails from DiL's iPhone at least 2 days after they were sent, so it does look more likely that the problem lies there.

I'm not sure if it's relevant, but I think that most of her emails are sent/received via her iPhone. I do all my emailing via a laptop.

I was wondering if anyone else has had problems of this type and if you have been able to do anything about it.