Validation of email

[Norman Khine]

Hello,
What is the best way to generate a long authentication string and email
this so that the user can reply and verify that the email address they
have provided is authentic, similar I guess to the way Bugzilla works?

Should this be server side or client?

How would one tackle an expiry limit on this - i.e. set the string a
time limit?

Any useful links of implementations in python are most welcomed.

Cheers

Norman