Attachment Size Limits

Attachment Size Limits

Attachment size limits are determined by your internet service provider and often by other gateways like in-house mail servers.

Like most policies of large communications services providers, e-mail file size limits are difficult to find and interpret. Many ISPs change their rules depending on the level of subscriber service. We assembled the list below from online and phone help desks at major U.S. broadband providers. For a definitive number, you may have to contact your ISP’s help desk.

AT&T: 25 Mb (webmail), 10 Mb (client) 
Cable One: 10 Mb
CenturyLink: 10 Mb
Charter: 10 Mb
Comcast: 15 Mb
Cox: 10 Mb
EarthLink: 10 Mb (webmail), 5 Mb (client)
Frontier: 3 Mb
Gmail: 25 Mb
Qwest: 10 Mb
Time Warner Cable/Road Runner: 20 Mb
Verizon: 8 Mb (webmail), 20 Mb (client)
Bright House Networks/Road Runner: 20 Mb
Windstream: 1Gb
Optimum Online/Cablevision: 20 Mb

Message Size Indicator

The message size indicator will display the total message size, including text and images.


You can set Postbox to warn you if you exceed this threshold in Preferences | Options > Composition > Advanced. Simply set the maximum threshold, and you will be warned when your message exceeds this threshold.