- Device compatibility
The sender has no control over what device or software the recipient is using and,
as of 2013, the majority of domestic users are receiving e-mail on smart phones or
tablets which probably do not have the software to view the attachment.
- Software compatibility
There are many versions of whatever software is being used. There is no guarantee
that the recipient is using a compatible version. However, the majority (possibly all)
devices can read pdf files.
Many e-mail clients, especially those running on smart phones or tablets, do not
automatically download attachments, doing so requiring an additional step or two
and, depending on bandwidth available (not much when out in the sticks using gprs),
this can take an appreciable amount of time. In fact it is usually not worth the effort.
- Version control
Having sent a word document as an attachment you get amendments returned then need to send
a revised version which is then redistributed. Which is the definitive version? A better
solution is to store the definitive version on a shared facility e.g skydrive (for Hotmail
users), google drive (for gmail users), dropbox , a web server, etc., then send a link to the file.
- Virus detection
Most reputable Internet Service Providers and e-mail hosting systems filter e-mail
for spam and viruses which involves unpacking the e-mail, subjecting it to various
filters and spam/virus detection systems, repackaging the e-mail and sending it on
its way. HTML e-mail as used by Hotmail, Yahoo, Gmail etc., is in itself an
e-mail attachment on top of the plain text e-mail headers, so adding another attachment
to the attachment increases the chances of it being mangled and slows the system down.