Hi Peter,

Firstly let me know that is this problem occurring with all the email messages or some specific emails?
Sometimes when you receive an email attachments with some unknown extension that is not allowed on email client, at that time you may face problem in opening those attachments. this is because these kind attachments can spread computer viruses and malware easily through email messages.

Below are the list of attachment extension that are not allowed over email client.
.ad, .adp, .crt, .ins, .mdb, .mde, .msc, .msp, .sct, .shb, .vb, .wsc, .wsf, .cpl, .shs, .vsd, .vst, .vss, .vsw, .asp, .bas, .bat, .chm, .cmd, .com, .exe, .hlp, .hta, .inf, .isp, .js, .jse, .lnk, .msi, .mst, .pcd, .pif, .reg, .scr, .url, .vbe, .vbs, .ws, and .wsh.

If you see email attachment with these extension, then kindly ignore those emails.


Thanks & Regards,
Anjlua