A. The server is designed to block attachment types which are seen as a danger
if they are not zipped up.
Some attachment types that are blocked are: .bat .src .exe. The reason for this
is that your mailbox would be flooded every day with viruses if this was not in
place. A few attachments that are fine without zipping up are: .gif .jpg .html .pdf.
Unfortunately, there is no way to turn this off so your only option is to zip your
attachment or doing the below.
B. Another reason could be the size of the attachment if you're sending an
attachment that is 10 MB or larger, it will fail due to the size. It is not wise
to email attachments this size because it can cause problems on the recipient
mail box also.
If you are sending it from webmail this limit is less than 2 MB.
A better option to get around these limits would be to upload the file to
your site and give out the link instead. You could even password protect
so the public cannot view or access the file.
You can upload the file using the Using File Manager