I've used Symantec EV and don't like it too much; a general antipathy towards Symantec products rather than for any sensible reason I'm afraid.
I generally tend to shy away from email archiving products for a number of reasons. Firstly, one can always look at better mailbox management policies. Secondly, I question if important info such as we're talking about here should really reside in the email system in the first place. Look at it this way: if somebody was on leave and an important doc was lurking in their email, what would need to be done and would you be happy doing it? Finally, check your data retention legislation - it may be the case that for email the owner of a record is the person who creates it, i.e. the original sender. If this is the case, the 20 odd people who have received it have no grounds for keeping it. In other words, I view archiving as moving the problem elsewhere.
User education is the best approach; get them in the habit of deleting emails that they don't need to keep, saving attachments to the file system, and so on. Have them understand that these documents aren't their own personal property, they belong to the company. My experience is that people tend to be hoarders so far as email is concerned, and once you get that sorted out you may find that the problem goes away on it's own (and saves a lot of money in doing so!)
If, and only if, after having done all that you still have email volume problems, then is the time to consider archiving.
