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Consider Hosted Exchange. That is what my clients use and have done for many years. That is the easiest way to keep up with spam control and provide good service at the same time.<br />
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For roll your own, look at Barracuda spam filtering and consider the use of grey list hardware.
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I am having 15+ years of experience. Handling major clients, my smallest customer is having 30K mailboxes. Large is above 200k mailboxes. <br />
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Now let me answer your query. For 200+ users GFI is enough. If you are looking for high end solution, you can look for Brightmail or SMG, Trend Micro or EOP from Microsoft. You can also have two layers, one layer on premises and another cloud. Like you have any AV/AS server on premises and then you can forward it cloud vendor like Messagelabs. This will add extra layer for scanning.<br />
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Also note, regularly updating spam definition patterns, helps to keep spam mails under control. You also need to restrict anonymous relay from your Exchange server. If you have Exchange 2010, enable restrict DL checkbox. That way external users won't be able to send emails to DL's.<br />
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Finally, as per my experience, spam can be controlled by creating custom spam rules regularly. It is a continuous process. As for each company spam definition is different. For some a X email is spam, however for some it is a valid mail.<br />
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Let me know, if I can help more.
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Cisco IronPort, ProofPoint are leaders both have on-prem and cloud offerings. &nbsp;MimeCast also has a good reputation but they are a pure cloud offering.
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GFI ME is not bad, and most mailfilters use the same technology. Adding &nbsp;greylisting to the mix may help, that needs to be done on point of entry of mail.
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GFI is not bad compare to what is was 15 years ago however &nbsp;many old problems (all or nothing approach with auto white list)<br />
1. auto white list never worked properly as even with &quot;out of office&quot; combinations added to the GFI registry key to exclude autoreply its still doesn't work properly and have bogus while list enters.<br />
2. Gray list doesn't work very well with emails coming from GMail or similar servers and we can't afford to loose customer emails<br />
3. Quarantine collects a lot of garbage as you can't place Antivirus check before attachment?????? and the only what do clean it up is to create search folders<br />
4. there is no way to make any logical combination of rules . Say white list + another rule etc.<br />
5. Directory harvesting is very hard to fine tune as if you set it by default with 1 wrong address you will through away perfect customer email with a single address error. when you star to make it 3 or 4 you skip a lot of spam and again you can not use any combination of directory harvesting and any other rule.<br />
and I can list you at least 5 more problems which were there for the last 15 years.
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can someone comment on <a href="http://www.PineApp.com" rel="ugc">www.PineApp.com</a>&nbsp;software?
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I have not heard of that one. My clients use Hosted Exchange and Microsoft Exchange but this one has not come up in my travels.
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We currently use MimeCast. Currently we have on-premise Exchange and MC works wonderfully with this. This year we will be moving to Exchange in the cloud with Office 365, but unless the MS offering can meet or beat what we get with MC, we'll stay with them. <br />
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Plus you get a lot of great extras with MC beyond what you're looking for - some are included some cost.
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We use (and offer) Mimecast, as it has proven not only incredibly accurate with respect to spam/virus protection, but easy to use for archiving/ediscovery and offers continuity services as well.
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We are currently using GFI Mail Essentials &nbsp;as an SMTP server alone with Checkpoint firewall anti-spam.<br />
GFI checks for, spam, viruses and attachment. They do a decent job in general but still use old 15+ year logic.<br />
we do host a couple of exchange servers with 200+ users. What would be a good &nbsp;Anti Spam with antivirus &nbsp;and attachment checking email filter possibly with email encryption to replace GFI ME. &nbsp;Google use resale Postini to non google apps users before. Very important this question is posted for a real expert with 10+ years of experience.<br />
&nbsp;thank you.
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We are currently using GFI Mail Essentials  as an SMTP server alone with Checkpoint firewall anti-spam.
GFI checks for, spam, viruses and attachment. They do a decent job in general but still use old 15+ year logic.
we do host a couple of exchange servers with 200+ users. What would be a good  Anti Spam with antivirus  and attachment checking email filter possibly with email encryption to replace GFI ME.  Google use resale Postini to non google apps users before. Very important this question is posted for a real expert with 10+ years of experience.
 thank you.

best email filter

Various techniques are used to prevent email spam (unsolicited bulk email). No technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate email (false positives) vs. not rejecting all spam (false negatives) - and the associated costs in time and effort. Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials.

AntiSpam

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.

Email Servers

Anti-virus software was originally developed to detect and remove computer viruses. However, with the proliferation of other kinds of malware, antivirus software started to provide protection from other computer threats. In particular, modern antivirus software can protect from malicious browser helper objects (BHOs), browser hijackers, ransomware, keyloggers, backdoors, rootkits, trojan horses, worms, malicious layered service providers (LSPs), dialers, fraud tools, adware and spyware. Some products also include protection from other computer threats, such as infected and malicious URLs, spam, scam and phishing attacks, online identity theft (privacy), online banking attacks, social engineering techniques, Advanced Persistent Threat (APT), botnets and DDoS attacks.