Forums mIRC Help Unique nick/alternate for every network

You could try using /emailaddr
If this doesn't work directly, you could also force a disconnect then a reconnect using a combination of the ON DISCONNECT and an offline timer.

I know how to change the e-mail address. That wasn't the question.

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see /help ON LOGON, you can hook into the connection process before mIRC sends out user info.

Just as a note by the way, you mentioned something about how mIRC should differentiate a variable from punctuation because it's "not alphanumeric". There is no rule that variables are only made up of alphanumeric characters. In reality, any of the 255 characters except $chr(32) and a few other specials can be used in a variable name: //set %x $+ $chr(9) xyz | echo -a $($+(%,x,$chr(9)),2) (chr9 is the tab character by the way) -- there is no way for mIRC to differentiate in this case.

In addition to argv0's post regarding the variables, I have yet to see a program that doesn't accept the . as an alphanumeric character, as it is used on a numeric basis as a decimal for numbers that could be displayed as a fraction, rather than a whole number.