By Ian Bush

PHILADELPHIA (CBS) – When it comes to checking e-mail, desktops and laptops are about to get left in the dust of smartphones and tablets.

A report from the e-mail research firm Return Path finds that mobile is about to pass far less portable ways of opening an inbox.

“As early as next month, we’ll see mobile overtake all other platforms.”

Tom Sather, a senior director at Return Path, calls it a matter of obsession with the devices that make it simple to check messages early and often — as long as they’re readable on mobile.

“We found a lot of people who are looking at images or e-mails that aren’t optimized for their mobile platform; they just delete it and move on.”

An important message for small businesses and other marketers: you only have one shot to make a good first impression on your readers, wherever they’re checking their mail.