Gmail not Truely “Unlimited “

Gmail has some unusual program policies which are infact in place so as to counteract and fight spam.
Sending limits

In an effort to fight spam and prevent abuse, Google will temporarily disable your account if you send a message to more than 500 recipients or if you send a large number of undeliverable messages. If you use a POP or IMAP client (Microsoft Outlook or Apple Mail, e.g.), you may only send a message to 100 people at a time. Your account should be re-enabled within 24 hours.Causes error(Gmail Lockdown in Secton 4)

POP or SMTP Users

Those who use POP or SMTP cant send a mail to more than 100 people at once, Failing this will cause Google to Block your Mail for 1 Day(550 5.4.5 Daily sending quota exceeded)

Broken Mail Addresses

Sendng a mail to a large number of wrong of non existent mail address will cause google to disable your acount.

Account Inactivity

Google will terminate your account in accordance with Section 9 of the Terms of Use if you fail to login to your account for a period of nine months