Re^2: input - E-mail address - how to check string ?

instead of 'try to send an email to that address' you can, strip the domain part, lookup that domain for MX record, establish an SMTP sesssion and issue a "RCPT TO" or "VRFY" command and wait for a '200 OK' answer. Less spammy.

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Re^3: input - E-mail address - how to check string ? by afoken (Chancellor) on Feb 26, 2015 at 18:40 UTC
establish an SMTP sesssion and issue a "RCPT TO" or "VRFY" command and wait for a '200 OK' answer. In our days, no sanely configured internet mail server will expose its account list by giving a clear positive or negative response to the `VRFY` or `RCPT TO` commands. Typically, the answer to `VRFY` is something like "I won't tell you" (my local Exim answers "252 Administrative prohibition"), and `RCPT TO` will be accepted no matter what mail account you try. The mailserver will decide after(!) the SMTP dialog how to handle that mail, and may send back a "mail not deliverable" mail. That may take hours or days, depending on the mail server configuration (greylisting). Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l] [select]

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Re^3: input - E-mail address - how to check string ?
by afoken (Chancellor) on Feb 26, 2015 at 18:40 UTC

establish an SMTP sesssion and issue a "RCPT TO" or "VRFY" command and wait for a '200 OK' answer.

In our days, no sanely configured internet mail server will expose its account list by giving a clear positive or negative response to the VRFY or RCPT TO commands. Typically, the answer to VRFY is something like "I won't tell you" (my local Exim answers "252 Administrative prohibition"), and RCPT TO will be accepted no matter what mail account you try. The mailserver will decide after(!) the SMTP dialog how to handle that mail, and may send back a "mail not deliverable" mail. That may take hours or days, depending on the mail server configuration (greylisting).

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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