That is strange. Some users may have mailbox filters/rules about which messages appear spammy, and having a sender spoof the sending address so it appears you are emailing yourself is one of the patterns people might set up. But I don't think that would be a built-in/automatic rule. You should be able to check your Yahoo! Mail filters and edit as needed using the steps in their help articles: * https://help.yahoo.com/kb/filters-organize-yahoo-mail-sln36699.html * https://help.yahoo.com/kb/emails-incorrectly-trash-wrong-folder-sln6265.html * https://help.yahoo.com/kb/fix-issues-yahoo-mail-filters-sln27270.html