How do I check mailbox spam set safe person sender

Hi I'm Brian and I'll try to help.

Since this forum is dedicated to using Outlook for iOS, I'll assume that's how you access your mailbox. However, it would help if you stated who provides that mailbox.

When you state that you aren't receiving some incoming mail, does that means it doesn't appear anywhere in the mailbox - not Inbox, not Junk Email, not any other folder? How, then, do you know it was sent to you?

If the messages are being filtered by your mail provider prior to reaching your mailbox, there is no setting within Outlook that can correct that. It's not an Outlook issue. You must contact the mail provider about it. If it appears in the Junk Email folder incorrectly, then you can use the Move to Folder option and you should be asked if you want to mark the sending address as safe. It works that way for me.