How to spoof is just a google away. There are so many ways that I think it's not a good idea to ask how. It's just something that is done by scammers.
As to your account, if you can log in and don't see changes it's very unlikely it's been compromised.
That all said, the current email system is decades old and will for maybe more decades be subject to spoofing. This could really upset folk that didn't know this.
re gmail.com
received email To: me@mydomain.com
with From: address "user@mydomain.com"
where user is not and never was a user of mydomain.com
(I am the administrator of the email account)
gmail marked it as SPAM
AVG marked it as containing a virus
review of downloaded html text of the message shows numerous javascript functions
also complete text of recent legitimate messages passed by mydomain.com
questions:
1. how is it possible to create fake From: address?
2. has my account at mydomain.com which resides with gmail.com been compromised?

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