Several types of e-mail addresses checkup can be performed. The number of checkup methods used affects checking quality and overall time of validation process. Let us focus on each method:

Syntax checking

Syntax checking consists of checking e-mail address for @ character and for allowed characters. The allowed characters are: '-', '.', '0'..'9', '@', 'A':'Z', '_' and 'a':'z'. This method of checkup is the fastest with average speed of checking reaching thousands of e-mail addresses per second. However, we recommend using it for huge mailing lists only just to make sure there are only validly spelled addresses in the list. Internet connection is not required when using this method.

Domain checking

Domain checking is performed by connecting to DNS servers and querying domain names of e-mail addresses (e.g. checking domain.com for existence for kate@domain.com e-mail address). Checked domains are marked in domains list in the following manner:

- if the domain name is invalid it is marked as Invalid domain

- if the domain name exists but does not have MX records it is marked as

- if the domain name exists and has MX records it is marked as

The speed of this operation is lower than in case of Syntax checking but way higher than in case of Complete SMTP checking. This method is recommended for mailing lists containing hundreds of thousands or millions of e-mail addresses. About one third of invalid addresses are being removed on this stage of checking.

Complete SMTP checking

The complete e-mail address checkup is performed by connecting e-mail server(s) specified in domain's MX records, returned by DNS server during querying or directly to the domain name mail server in case that MX records are not found. Upon connecting to server the program tries to send mail to e-mail address being checked for validity. If the server responds with mailbox available message the e-mail address is marked as Valid, otherwise as Invalid - no mailbox. The conversation to SMTP-server is displayed on the log-panel located to the right. Syntax checking and Domain checking methods are used prior to Complete SMTP checking.

This type of checking gives the most realistic results, however it takes reasonably large amount of time to complete such check. The Complete SMTP checking method is recommended for mailing lists with no more than a hundred thousands of e-mail addresses. About two thirds of invalid addresses are being removed on this stage of checking.

Several types of e-mail addresses checkup can be performed. The number of checkup methods used affects checking quality and overall time of validation process. Free to try it.