Along with every mail i send avast tag is there

You're referring to the "AVAST" tag that appears in the headers of every email you send.

The "AVAST" tag is a digital signature added by your email client or email service provider to verify the authenticity and integrity of the email. It's a way to ensure that the email hasn't been tampered with or altered during transmission.

The "AVAST" tag is a part of the DKIM (DomainKeys Identified Mail) protocol, which is a method for authenticating the sender of an email. DKIM uses a digital signature to verify that the email was sent by the claimed sender and that the email hasn't been modified during transmission.

When you send an email, your email client or email service provider generates a digital signature using your domain's private key and adds it to the email headers. The digital signature is then verified by the recipient's email server, which checks the signature against the public key associated with your domain.

The "AVAST" tag is a specific part of the DKIM signature that indicates the email has been successfully verified. It's usually displayed in the email headers, and it looks something like this:

"DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com; s=selector1; h=from:to:subject:date; bh=...; b=..."

The "AVAST" tag is usually displayed in the "b=" part of the DKIM signature, which represents the base64-encoded digital signature.

So, to summarize, the "AVAST" tag is a digital signature added to your emails to verify their authenticity and integrity. It's a part of the DKIM protocol and is used to ensure that your emails haven't been tampered with or altered during transmission.