iOS e-mail app without automatic downloading of large e-mails It will also help me if you can write e-mail clients without this feature, so I don't need to try them myself

People keep sending me e-mails with pictures embedded in the text. While this is nice in principle, the problem is that those pictures have some mbyte in size each and together they eat up my cellular data volume.

Unfortunally, you can't tell iOS Mail not to load e-mails above a certain size (or to download those pictures automatically). You can switch off downloading images from remote servers (I did that), but that doesn't work for pictures embedded into the e-mail. Also, attachments of a certain size are not automatically downloaded, but somehow pictures are not considered to be attachments.

MacOS Mail has the possibility to set a limit for POP accounts, above which a confimation is needed before download. Why on earth not on iOS.

I also tried spark as an e-mail client, but I don't find that option either. And I don't find it in the description of any e-mail app.

Is there an alternative e-mail client to support this feature?
I think you can't stop the whole email downloading.

This is because an email is a stream of text the format is defined in this RFC. The programs that transmit and receive the email do not look at what the data is in the body of the email and so have to send all or nothing.

The files downloaded from other servers are represented in the email body as just text containing the name of the external file (a URL).

The mail client (the app on your iPhone) is the only software that looks at the body and it recognises certain plain text that the text after it is an encoded image.

Apple's mail clients including mail on the iPhone allows the sender to decide if large attachments are not put directly in the email body but held in iCloud as a external file so take up the small space as other external linkss.. Apple email attachment document.

There is a reason to use text only email :)