jueves 15 octubre 2020 :: 1630hrs (UTC +01:00)
This won’t help your problem though may help you understand what is going on.
We appraise all our client company sysadmins of this and cover any possible unforseen eventualities with a contact disclaimer before we accept them as clients.
With Apple Mail the sender cannot alter the way the recipient’s email client decides to format email message.
If recipients are using a 3rd party client, (not Apple Mail) then it is known they completely hack the email.
There are some workarounds, if that is the case.
The sender needs to make sure they have Windows Friendly and Attachments set in the Edit>Attachments menu.
When composing an email, change the font when you begin composing. If you leave the default (Apple) font without changing it, the message is interpreted as plain text by the recipient client. It then uses its default display font of a particular client.
If you really need a message displayed exactly as you intend, create a PDF and send that.
Email dates back to the very start of the Internet and was originally only able to support ASCII with no formatting. Over time email changed with now three main content types, plain text ( ASCII), Rich Text Format (RTF), and HTML same as a web-browser. However just as various word-processors will show slightly different results for the same RTF, and just as different web-browsers show slight or even significant different results for the same web-page code different email clients can show different results. Even different versions of the same client all running in Windows / macOS can produce different results.
Even though there are rules and standards that should help the reality is that many email clients implement the rules differently or make outright errors in doing so.
Apple Mail has been particularly bad at this and still is.
¡Saludos desde la soleada España!