blog.imm.cnr.it

p7m files are digitally signed documents and Mozilla Thunderbird manages those attachment with ease, displaying it in the e-mail body if positively recognized. Unfortunately for Italian users, maybe due to a not standard application of file format, when received a message with one or more file attachment of type application/pkcs7-mime (.p7m) is impossible to see the file and to save it.

It's a known issue (see bug 243833) and it's possible to fix installing the P7MONadd-on.

References:

https://www.easypc.altervista.org/2017/08/fix-per-thunderbird-che-non-visualizza-gli-allegati-firmati-con-estensione-p7m/

https://addons.mozilla.org/it/thunderbird/addon/p7mon/

https://thunderpec.wordpress.com/2014/07/24/thunderbird-31-e-p7m/

https://koolinus.wordpress.com/2011/03/29/thunderbird-and-the-p7m-files-attachments/

https://forum.mozillaitalia.org/index.php?topic=69117.msg479731#msg479731

https://forum.mozillaitalia.org/index.php?PHPSESSID=cg7rnv9505rjqisco50qok0av1&topic=58448.0