Nico's Mailer uses the concept of a "mailing list". A mailing list consists of:
- The message itself, having a subject line and a message body.
- A list of recipients.
- A number of file paths, each pointing to an attachment file you
want to send along.
- Some settings to control the sending process.
From the File menu you can load and save these four parts as a single mailing list file.

A message is sent to each recipient individually: there is no sign in the message of the fact that it is sent to more recipients.

Both subject line and body of the message can contain so called macro's. A macro is a character string representing an attribute of the recipient. For instance: If the body contains the macro %firstname% this will be replaced, just before the message is sent out to a recipient, by the first name of that recipient, as you specified it in the list of recipients. This way you can send out individualized messages.

Nico's Mailer can send HTML mail.

You can have Nico's Mailer show you a preview of the message just before the actual sending takes place, but after the macro's are expanded. From the preview you can make modifications to that particular message, cancel the message, or abort the whole mailing.

Messages can be delivered via your ISP's SMTP server, but also using a feature called Direct Send, which puts the message right into the recipients mailbox. Advantage: instant feedback about the send operation, and your own mailbox will not be filled with messages about failed deliveries. This Direct Send option is also great to validate e-mail addresses.

In the list of recipients Nico's Mailer keeps track of the mailing result for each individual recipient. Later on you can ask Nico's Mailer to try again for only those recipients for which there wasn't success.

Nico's Mailer is fully multi-threaded, which means a number of send operations can take place concurrently in the program, which greatly enhances performance of course.