The best replacement for attachments is enclosures.

The best alternatives to attachments are rated as following:
★★★★★  enclosures
★★  exhibits
★★  appendices
★  hyperlinks
  mtom
  annexes
  appendixes
  links

Your alternative for attachments is not listed? Suggest!
Speaking about attachments, one probably shouldn't forget about mail merge.

Other search terms related to attachments and their ratings are:
★★★★★ mail merge
★★★★ mailchimp
★★★★ invisalign
★★★ ipad email
★★★ google forms
★★★ outlook
★★★ mailx
★★★ sendmail
★★★ mac mail
★ opening email
★ e-mail
php mail
unix mail
mailto
emails
email mail merge
You have in mind a companion for attachments and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of attachments in all years. Click on graph for more.
attachments
enclosures
exhibits