What is x mailer

X-Mailer is a field in the header of an email message that identifies the email client or program that was used to send the email. It is a standard field in the email header, and it is used to provide information about the email client, such as its name, version, and operating system.

The X-Mailer field typically contains information in the following format:

X-Mailer: ()

For example:

X-Mailer: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2

In this example, the X-Mailer field indicates that the email was sent using Mozilla Thunderbird version 68.4.2 on a Windows 10 operating system.

X-Mailer is not a required field in the email header, and it is not used by most email servers or clients to determine the authenticity or validity of an email message. However, it can be useful for debugging and troubleshooting purposes, as it can provide information about the email client and the environment in which the email was sent.

Some email clients, such as Microsoft Outlook, may also include additional information in the X-Mailer field, such as the user's name and email address. However, this information is not standardized and may vary depending on the email client and its configuration.