Askimet is a bit strange....
On a small forum I co-admin that uses askimet we’ve found the only way a few people could prevent all their posts being mis-dentified as spam was to give them admin rights so they could authorise their own posts as “OK, not spam”. Once they’ve authorised one or two of their own posts they can then be reverted to a “normal” user and askimet happily lets them post from then on.
For some unknown reason they have to be the admin that authorises their own posts for this to work.