How the iPhone chooses which emails to sync

When you set your Exchange account to sync email on an iPhone, you set “Mail Days to Sync” to 1 Day, 3 Days, 1 Week, etc. Turns out this is syncing mail that was received within the last 3 Days, not sent within the last 3 Days. This is a crucial point when you migrate an email account. 

In my new Zoho email account, all 20,000 plus emails in my box are now marked as “received” yesterday. As such, I now have 20,000 plus emails showing up on my iPhone. One could argue that Zoho shouldn’t handle the received date that way but it is a defensible decision: the mail was received yesterday.

The correct “Sent” date is what displays in the iPhone’s Mail UI (not the received date), so it didn’t ruin the integrity of my messages, but it did reveal this little detail about how Apple chose to implement the mail syncing feature: Display the sent date, but sync based on the received date.

So for two more days, I’ll have every email I’ve received since 2003 handily available in my pocket.