I'm using Mozilla Thunderbird for my email, and have been for many years. I went to check my mail this morning, which told me I had seven messages. I clicked "get messages" like usual, but it only downloaded four- after that indicating there were no additional messages.
After sorting those out, the "you have mail" icon pops up, so I click the "get messages" button again. The dialogue box at the bottom of the frame tells me it's downloading 1 of 4 messages... which is a repeat of the last of the first four.
It's not spam, technically, but it's just an auto-generated sales blurb from Storenvy, where I have my online store, telling me about some upcoming site-wide sale.
I delete that, hit "get messages" again. It again tells me it's downloading one of four messages- the same ad from Storenvy. Click again, I get another copy. Click ten times, I get ten copies of the exact same email.
All the while, the (presumably) other three messages aren't downloading, and I apparently have no way of accessing them.
What could be causing that, and how might I go about fixing it?