thanks for that post/pm. i wondered what was going on there. i changed my interval settings on my computer to check every 15 minutes instead of every five, and i hope that will fix that issue. i'm accessing yahoo mail via pop and not imap, which allows for mail.app to retrieve my mail. the base yahoo account doesn't let you do that, so i had to upgrade to the mail plus account.
yahoo really just needs to support imap and the problem would be solved. i am really angry they have not enabled push on their small business accounts that are paid, when it's functional for free accounts. it doesn't make sense that they offer imap push for iphone only? if you feel like calling them and complaining about their lack of imap support for desktop computers, call: 800-318-0783
feature-request@yahoo-inc.com
the cs rep said that they usually comply if enough people request a feature. he did not know about the imap. i am sure it is imap, the server for the iphone is imap.apple.mail.yahoo.com. i can't imagine people haven't been requesting this feature for the ages, but i guess now that it is available strictly for iphone yahoo mail users free of charge it is baffling why paid users and full imap are not available. even if it were for an additional fee. the ability to have perfectly synchronized computers across multiple devices is priceless.
https://forums.macrumors.com/threads/323113/