Short Tip: Extract attachments from multipart messages

Sometimes e-mails are stored as a plain text file. This might be due to backup solutions or as in my case, sometimes I have to save e-mails in text format because the client has issues with more complicated S/MIME mails with attachments.

In such cases the text file itself contains the multipart message body of the e-mail, so the attachments are provided as base64 streams:

--------------060903090608060502040600
Content-Type: application/x-gzip;
 name="liquidat.tar.gz"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="liquidat.tar.gz"

qrsIAstukk4AA+17Wa+jSpZuPfMrrK6Hvi1qJ4OxsfuodQU2YLDBUJDGrvqBeR7MaPj1N7D3
OEmSxO8Wq7+3Y48dTWvXi8XvvKj8od6vPf9vKjWIv1v7nt3G/d8rEX5D/FdrDIxj2IrUPeE/
j5Dv4g9+fPnTRcX006T++LdYYw7w+i...

These data can be extracted manually, but that’s a wearisome task. It’s easier to use munpack, which can easily extract attachment(s) out of such text files and write them into a proper named files.

$ munpack -f mail.txt
liquidat.tar.gz (application/x-gzip)

Short Tip: Convert PEM files to CRT/DER

Within the Linux eco system certificates are often exchanged in PEM format. However, when you have to deal with other, most often proprietary eco systems you must be able to export the certificates in other file formats. For example, if you have certificates stored as PEM files and need to export them in DER format which often ends in .crt, .cer or .der you can use openssl to rewrite them:

$ openssl x509 -outform der -in MyCertificate.pem -out MyCertificate.crt