Hi

My immediate reaction is no.

A T1 line is 1.54 Mbps

A T3 line is 44.736 Mbps

 

Sounds like you have symmetrical service, but its not a T3 line.

3Mbps is about the slowest internet connection available now. Yes, it might be digital (if it is symmetrical) , but its still slow. Standard household service from cable is like 10-15 Mbps now ? Here in Hawaii you can get 35Mbps - 100Mbps standard, and even up to 300 Mbps --- at home ! your cell phone on 4G probably gets in the neighborhood of 12 Mbps

 

you and your 150 users, are you already running an email system ? or is this a new setup with a new startup company ? If it is an existing setup you want to move, then what is your existing email load ? How many emails a day, how many an hour, what is the connections total bandwidth consumed ?

 

Is there any email traffic internal on the network ? or is all of the email going out over the internet connection ?

 

Are you users all in the same domain and company ? or are these going to be different domains ?

 

Lets say a user sends a 5 meg (MByte, not Mbit) attachment that they need to send out to 30 people in the company. All 30 have to download that 5 Meg file, 150 Meg total.