Steps to sync sent folder in iPhone

Step 1: Launch the Settings app

Step 2: Choose Mail Contacts and Calendars

Step 3: Select the account with which you are having trouble syncing the Sent folder

Step 4: Under IMAP tap on your Account. (NOTE: If it says POP, then you have to delete the account and re-add it as an IMAP account).

Step 5: Choose Advanced at the bottom

Step 6: Under Mailbox Behaviours, tap on “Sent Mailbox”

Step 7: Ensure that the folder called “Sent” is checked off under the “On the Server” section

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