Cannot send emails via iPhone/iPad. Only via Cox Web Mail. ALL SETTINGS ARE CORRECT

Cannot send emails via iPhone/iPad. Only via Cox Web Mail. ALL SETTINGS ARE CORRECT w IMAP. Have uninstalled & reinstalled multiple times to no avail. Have spoken w Cox representatives more than once & they affirmed all settings on my end are correct. Say it’s an Apple issue. Been through support w Apple more than once, everything set correctly, they say it’s a Cox issue. Tried again TODAY. This has been this way for over a year & a half. Frustrating to have to use Cox Web Mail & opening a web browser to send an email VS. simply hitting the mail icon on my iPhone/iPad to do so. Frustrating beyond belief is an understatement. Hope Cox or someone can figure this out.