Using your ISP email address (or free email account) is acceptable for someone who isn’t running a business. But if you are in business and have a domain, it looks unprofessional to use your ISP for business communication and using a free email account does nothing for your business image or credibility.

So, why do businesses use their ISP email address rather than an email address from their domain? There are a number of reasons why people might not be using their domain email address.

Email Configuration
The first reason relates to email software configuration. Often people just don’t know how to make the necessary changes in their email software so that email can be sent and received via a POP3 account.

Hosting Provider Services
The second could be that while the people actually know how to change the outgoing email address and company details in their email software so that email appears to be being sent from their business (i.e. This e-mail address is being protected from spam bots, you need JavaScript enabled to view it ). However, their hosting provider doesn’t provide SMTP mail server facilities.

Email Relaying
Similar to the above, people know how to make changes to their email software but their hosting provider doesn’t allow SMTP email relaying for other domains through their server.

ISP Issues
Many ISPs are blocking what is called "Port 25" which is the port normally used to send e-mail. They are doing this to cut down on the amount of spam that is sent from their networks.

Port 25 blocking allows ISPs to block spam sent out through their networks, but it tends to punish the innocent that have a need to send through e-mail servers other than those belonging to their ISP. The ISPs that block port 25 require their SMTP server to be used instead of the remote SMTP server or a SMTP server running on your computer.