what i would suggest is when they sign up, get the current seconds from 1970, and write it into the database. Also in the dtabase add a row called confirmed. confirmed will either be yes or no. no as default. Then if you add a script in a webpage viewed frequently, you could tell the script to get the time from 1970, then take the time from the date subscribed in the entry. If the subscribed date is over 7 months gone, tell it to send a e-mail to the persons e-mail in db, and if the e-mail is sent successfully set te confirmed row to yes
make sure that you only select entries from the database that have checked as no.... can you understand that?