When you are on a shared server with others and are using your web hosting company’s SMTP to send out there are deliver-ability issues that can happen from time to time. These issues spring from two places usually.
1. Your site gets hacked and starts spamming
2. Someone else on the server starts spamming.
When this happens, the mail getting sent out from the web hosting company’s mail server can start becoming blacklisted. Blacklisted is just what it sounds like… in this case mail is not allowed to be delivered to other networks who check the blacklist providers records to see if you’re on them and they stop your mail from being sent to their users. For them, this helps reduce spam and nonsense mail sent through their mail systems.
What does the hosting company do about it?
If this happens we identify the source of the spam or issue, resolve it, suspend it, or shut it down, and then submit to remove any blacklists that have occurred. There are over 200 RBLs (registered blacklists) for email. Typically the least responsive companies are microsoft, att (bellsouth and their networks) who take longer than others to allow mail to start being sent through again once they are notified that the spammer is stopped. Once removed from the blacklist mail starts to be accepted through the networks again.
Using Webmail or Server Relays:
When you use the SMTP from your web host, you are using a “relayed” mail send out. This means that we are relaying the mail to your intended recipient instead of having the mail come directly from your ISP or original source (which is generally more preferred by mail servers). Many ISPs prefer mail to come from the source over port 80 but relayed mail is sent via port 25 (or in our case port 26 to make it more preferable to other ISPs). ISPs tag port 25 as a “known” relayed send out and mark it as less authentic and give it less trust for delivery.
As a result, using your ISPs mail server for SMTP is the best practice to ensure the best deliver-ability. It will still go out showing the email as coming from your domain name (if you set it up that way in your mail client).
So, in the meantime, if you are not traveling and want to make sure your mail is able to be delivered to those networks you can set your SMTP on your mail client to use that of your ISP. That way outgoing mail is sent via your ISP and not through a relay. You would simply call your ISP, ask them to give you your SMTP settings for your mail, and then use that to send out.