I’ve been using the the iPhone mail app to sync my contacts, calendar and emails through exchange server. One thing I noticed was that there was no setting to limit the file size of every email received. Even if you set the email limiter on server side, the iPhone wouldn’t recognize it. This is very crucial especially to KB/bandwidth based data plans since every kilobyte cost money. After getting frustrated about it, I began to study the behavior of the iPhone mail app and realized that Apple automated everything to prevent users from making mistakes but sacrificed user control.

So how does it work?

WIFI

If your iPhone receives the email through wifi, the iPhone will automatically download any email below 1 MB (regardless of any setting like number of preview lines and etc). So if you have an email with 999KB worth of text and 800KB attachment file, iPhone will download them all even if you didn’t view the email. The number of attachments do not stack, it will download any attachment below 1MB and let you manually download beyond 1MB whether you like it or not.

3G/GPRS

If your iPhone receives the email through GPRS/Edge/3G, the iPhone will automatically download any email below 125KB. The difference here is that if the email content does not have any attachment and it is below 125KB, the iPhone will download it automatically even if you didn’t view the email. But if the email has an attachment, the iPhone will just download the header(will show the preview lines if set but will not download more than that). When you start to view the email with attachment, that’s the time where the iPhone starts downloading anything below 125KB. The rule is the same with wifi where the attachments do not stack up, each attachment will be checked if it’s under 125KB.

Hopefully I managed to give the iPhone mail users insights on how it works with exchange server.