Is anyone aware of the length of time a company must honor a person's request to unsubscribe from email? If someone unsubscribed from our emails 4 years ago is that request still relevant?
What is the "statchute of limitations" on unsubscribing?
You need to contact your legal counsel, but in the strictest jurisdictions there's no expiration at all. The user's preference does not change on its own.
If someone has unsubscribed then you can't resubscribe them. It's up to them to opt back in if they want to. I would be very wary of sending an email to people who have unsubscribed. In Europe you would be breaking lots of rules and next year with GDPR you could face fines of 20 million Euro or 4% of global turnover. Do you have a huge list? Could sales not give them a call and ask them if they could send them some information. This could be done on a one to one basis without breaking rules. If a sales rep was to talk to them and then send them a relevant and personal email it might encourage them to opt back in.
Like Sanford mentioned, I would definitely do my due diligence and seek legal advice if possible.
I have never heard of a statute of limitations for Unsubscribe.
CANSPAM and other laws are NOT the same as the Do Not Call List in the US, which does have some sort of expiration on the block. But do check with your legal counsel.
Frankly, even if you were permitted to send again after X time, why would you? That person was clear they weren't interested. Find people who are interested.