Quest email service tag

Here are some common email service tags:

Transactional Email Services

1. Mailgun - x-mailgun-original-to and x-mailgun-original-from
2. Sendgrid - X-SMTP-API-User and X-SMTP-API-Key
3. Amazon SES - X-SES-Message-ID and X-SES-Source
4. SparkPost - X-SparkPost-Message-ID and X-SparkPost-Source

Marketing Email Services

1. Mailchimp - X-Mailchimp-Original-Request and X-Mailchimp-Original-Request-IP
2. Constant Contact - X-Constant-Contact-Message-ID and X-Constant-Contact-Source
3. Campaign Monitor - X-Campaign-Monitor-Message-ID and X-Campaign-Monitor-Source
4. Klaviyo - X-Klaviyo-Message-ID and X-Klaviyo-Source

Other Email Services

1. Gmail - X-Gmail-Original-Message-ID and X-Gmail-Original-From
2. Outlook - X-Outlook-Message-ID and X-Outlook-Source
3. Yahoo - X-Yahoo-Message-ID and X-Yahoo-Source

These tags can be used to identify the email service provider, track email campaigns, and troubleshoot email delivery issues.