OP, if you had a valid email address and your email account expired for whatever reason (didn't use it for one year e.g. and your email provider deleted your email account if they have such an account usage policy requiring a minimum use within a certain time to keep the account alive), it was detected by the forum when sent emails to your email account bounced back as undeliverable. If this invalidation of your defunct email address by forum software didn't happen, it would be possible that someone else registers your deleted email address and takes over your Bitcointalk account by requesting a password reset via email.
(At least theoretically, because the adversary would need to know which email address belongs to your Bitcointalk account. But who knows where you may have spilled the beans...)

It's possible you didn't notice that your email address expired. Well, now it's the time to fix this issue and change your account's email address to one that actually works. You may need it in case you forget your password.