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Are email headers/sources affected by service providers or email clients?

When I draft and send an email from my Thunderbird, is the source of that message unchanged when it is received by the other end? For example, let's say I send from Thunderbird to my Gmail SMTP, which then contacts Yahoo servers to send my email to my colleague's Outlook. When they view the message headers/source, should it be identical to my source? Or do the services or clients adjust them somehow?

Thanks!

When I draft and send an email from my Thunderbird, is the source of that message unchanged when it is received by the other end? For example, let's say I send from Thunderbird to my Gmail SMTP, which then contacts Yahoo servers to send my email to my colleague's Outlook. When they view the message headers/source, should it be identical to my source? Or do the services or clients adjust them somehow? Thanks!

Chosen solution

It should. However, to be absolutely sure the received message is identical with what you sent, you'd need to digitally sign the message, and the recipient would need to verify the signature. I suppose it would help if you could explain what's your problem in the first place.

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Chosen Solution

It should. However, to be absolutely sure the received message is identical with what you sent, you'd need to digitally sign the message, and the recipient would need to verify the signature. I suppose it would help if you could explain what's your problem in the first place.

Thanks christ1. I have what I think is an encoding error somewhere between Thunderbird and Outlook (or other Thunderbird clients?), but I wanted to get this bit clarified before I grab a bunch of headers I might not need. I will try to keep things tidy and post them in a new question. Thanks again.