Patchy success at identifying attachments as viruses

We regularly receive e-mails which are attempts to introduce the ransomware virus (where identified, it’s “JS:Lockydownloader”) onto the computer (averaging at least one a day, often more). They’re fairly easy to spot, but I’m concerned that Avast is only identifying about a quarter of them. The attachments purport to be of various file types - is this why Avast isn’t highlighting them?
Is there a safe way to examine the attachments in case they’re legitimate? And can Avast be “trained” to spot those it’s currently missing?

Submitting Malware Samples: https://www.avast.com/faq.php?article=AVKB258#artTitle

Suspicious file(s) can be uploaded and tested here virustotal.com / metadefender.com / jotti.org
If scanned before, always click rescan for a fresh result
Use the additional tabs for finding additional file info after scan