What is verification code of Gmail?

email verification helps an email recipient know that the sender address information in an email message is actually that of the sender.

Like in a regular postal service letter, the from addressis merely text put into mail by the mail program and spammers can have it say anything they want. In postal service mail you can still try to verify its sender by examining the cancellation over the postage stamp. If it is readable, it can tell you at least the general location or post office from where it was mailed.

An email has a header section with additional information that can tell where the email originated and how the email came to you. Some of it can be faked, but not all of it. Some emails also have verification information such as DomainKey (DKIM) and/or Sender Policy Framework (SPF) that verifies the email sources and if the email source is that of a known source of spam or malware. Failure to properly verify an email can result in the email message being dropped(lost) or being routed to a spam or junk folder. It all depends on your email provider.