First of all, select Settings > Mail then scroll down to Blocked Sender Options. Tap that and make sure the option is set to Move To Trash. This should guarantee that you will not see messages from blocked senders. But the bad news is this … Spammers keep using different variations of an email address and each has to be blocked individually. For example, look at the two below:
- Sender1234@domain.com
- Sender12345@domain.com
In my experience, if I keep blocking the particularly nasty messages, eventually they stop coming. But it takes a while.
I just thought of one more thing … You can select Settings > Messages then set Filter unknown senders to green (yes). This way at least, your Unknown Sender messages will be in a folder of their own. You will not see them when you open Known Senders.