How can I stop my email being blocked as spam?

I have my own small company that deals with big corporate customers. Many of these, plus others, have told me my email keeps going to their junk folders. I have my domain DNS hosted on a shared reseller server (Hostgator) where my web site is hosted, and I use Exchange Online (or Office 365 or whatever MS is calling it this week) for email service. The MX record point to the MS server as per the instructions provided by MS. There is also a correctly setup SPF record.

How can I stop my email going to junk or at least test my outgoing email to see what is getting it classed as spam? Would signing my email with a digital certificate help?

Thanks.

P.S. I am NOT a spammer!!!

One of the useful tools to resolve this issue would be e-mail headers. Often they can reveal WHY that e-mail went to spam folder. E-mail headers contain full information on what happened to e-mail while it was in transit. Often you will be able to see results of anti-spam processing which was done on the e-mail. And often it is full report which can tell you why this e-mail was considered as spam by that software.

In this example we can see header X-Spam-Status: which set to score=3.7. This header is just information that anti spam software analyzed the e-mail and based on the settings it has made the decision that this e-mail has spam score 3.7 It is semi-arbitrary scale and amount of spam points which e-mail will get depends on the software.

Here is another example:

X-Spam-Status: Yes, hits=27.3 required=5.0
 tests=AS_SEEN_ON,BASE64_ENC_TEXT,CLICK_BELOW,CLICK_BELOW_CAPS,
 CLICK_HERE_CAPS_LINK,CLICK_HERE_LINK,CTYPE_JUST_HTML, DCC_CHECK,
 DIET,FOR_FREE,HAIR_LOSS,HGH,HIDE_WIN_STATUS, HTML_COMMENT_UNIQUE_ID,
 HTML_WITH_BGCOLOR,JAVASCRIPT_UNSAFE, OBFUSCATING_COMMENT,
 OPT_IN,RAZOR2_CHECK,RCVD_IN_DSBL, REVERSE_AGING,SPAM_PHRASE_05_08
 version=2.43
X-Spam-Flag: YES
X-Spam-Level: ***************************

Here we can see that e-mail was evaluated to have 27.3 spam score (hits=27.3). This software was configured to consider any e-mail with score more than 5 to be spam (required=5.0). So what it does in this case? It sets flag X-Spam-Flag to YES. This is just evaluation. Now you can set filter on your e-mail client which will put any e-mail with X-Spam-Flag: YES to the spam folder.

I just gave you one example of how e-mail headers work. Probably you will be able to see reason why your e-mails are considered to be spam.

Ask people who receive your e-mails to send you back e-mail headers for research. Every modern e-mail client should be able to get those.

I am not promising it will work for you. But e-mail headers and server logs - are first things you should look at while resolving e-mail issues.

Before you can fix the situation, you need to first determine the reason that your mail is getting labeled as spam.

One likely reason is that another website, with whom you are sharing an IP address (for outgoing mail) on your shared server, is sending spam, and this has caused your shared IP address to get blacklisted.

You can check if your mail server IP address is blacklisted or not using a tool such as this: http://www.mxtoolbox.com/blacklists.aspx

If your current mail server IP address is blacklisted, then you need to switch to (or relay through) a different mail server whose IP address is not blacklisted.