Learning how modern laws and mailing systems work can assist you in not being marked as a source of SPAM.
What happens over time is that people will mark your address as a SPAM source, this is not a problem on individual peoples computers, they will just no longer see your mails. On systems like gmail and hotmail however when a mail is marked as SPAM by enough users your address is marked as a SPAM source and people will no longer see your mail unless they have purposefully whitelisted you, your mail automatically will get redirected to their SPAM box’s. At this point your will need to change e-mail address to make sure people receive your mails once again.
Just some information to hopefully help you keep your e-mail from being marked as a SPAM source.
Unsolicted emails now have a legal definition and must meet certain requirements.