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Editorial Team
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Asked: 2026-05-27T10:16:56+00:00

I wrote a C++ application that needs to send emails. It does this by

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I wrote a C++ application that needs to send emails.

It does this by calling

/usr/sbin/sendmail -f [sender] -t

and then writing the mail headers and body to the standard input of the sendmail process.

Everything works fine – except for umlauts or other non-ASCII characters.
How can I make them working correctly?

I already tried to set

Content-Type: plain-text; charset=ISO-8859-1

as a mail header and also 

Content-Type: plain-text; charset=UTF-8

didn’t change anything. Seems like this header is ignored.

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1 Answer

  1. Editorial Team

    Anything other than ASCII in an email message should typically be encoded either as quoted-printable or base64. The Content-Transfer-Encoding and Content-Type headers are then set accordingly so that the recipient knows how to decode the message back to non-ASCII text.

    Here’s a bash example that illustrates how this can be done on the command line:

    #!/bin/bash
message="Hellö ümläüts"
encoded=$(base64 <<< "$message")

/usr/sbin/sendmail -t <<< "From: sender@example.com
To: recipient@example.com
Subject: Dear friend
Content-Transfer-Encoding: base64
Content-Type: text/plain; charset="utf-8"

$encoded"

    You need to specify whatever character encoding was used to convert the string to binary before the data was base64 encoded.

    This example uses utf-8, because that is a common platform default so most shells would use utf-8 when converting the string to binary and passing it to base64 on stdin.

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