I think 15 months is fair. After 12 months of inactivity the user receives emails saying their account will be deactivated if they do not log in. It could work like this:
12 months you get an email
30 days later, a reminder
30 days later, a reminder
15 days later, another reminder
7 days later, another reminder
4 days later: "Warning your account will be deactivated in 72 hours if you do not login!"
I think 15 months is fair. After 12 months of inactivity the user receives emails saying their account will be deactivated if they do not log in. It could work like this:
12 months you get an email
30 days later, a reminder
30 days later, a reminder
15 days later, another reminder
7 days later, another reminder
4 days later: "Warning your account will be deactivated in 72 hours if you do not login!"