RoboMail can work with different ISP.

In menu File > Settings > Sending Settings, you can specify your ISP's SMTP server settings.
Or you can leave all the fields blank, RoboMail will setup a builtin SMTP server on the machine and send emails.

You can also adjust the sending speed in menu File > Settings.
The speed can be set between 1 email per minute or the fastest 60 emails per minute.

The port 25 is the communication port of email sending. Different email servers are communicate with port 25.
If your ISP block port 25, you cannot use your own SMTP server to send emails as the communication is blocked.
You can only rely on your ISP SMTP server to send out email.  

New Buyer Wrote:I want to send out a list of about 1,000 client emails.  I am using PCCW ISP, is RoboMail works with this ISP?

What is Port 25?  What happens if this ISP blocked Port 25?

Thanks.