If you mean operating an email forwarding service, I strongly advise against it. I also suggest not using a webserver to relay directly to destination MX hosts.
Routing all outbound mail through a reputable smarthost, however, is a good idea. You will want to use a provider configured in a way that will allow you to readily identify the source customer in the event that you need to address any abuse issues.
Yes, I recommend that you use an SMTP, I use Amazon SES and it works wonderfully, the IP does not fall into a blacklist and the emails do not go to spam.