Email addresses verification
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 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 is performed by connecting to DNS servers and querying domain
names of e-mail addresses (e.g. checking domain.com for existence for
firstname.lastname@example.org 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.