Incoming SMTP is how most mail systems on the Internet work. With SMTP, the sender's mail system sends the message to the recipient's mail system, rather than the recipient's system collecting it from the sender.
VPOP3 works fully with incoming SMTP. In fact, on a fresh installation, it will work with incoming SMTP without any setting changes other than telling VPOP3 the local email domain. There are generally other things that you will need to do so that incoming SMTP works correctly, but those are all outside of VPOP3.
Incoming SMTP has two main advantages over other methods such as POP3 collection:
•Messages generally arrive as soon as the sender sends them, rather than at the next "poll time"
•If messages contain BCCs, those will always work with incoming SMTP whereas there can be problems with BCCs with shared POP3 mailboxes.
For an incoming SMTP mail feed to work, there are several requirements
•You must have your own email domain (eg 'mycompany.com') and be able to configure DNS records for that domain.
•You must have a static IP address on the Internet. Senders need to know where to send mail to you, so if you have a dynamic IP address they won't know where your mail server is. (You could, theoretically use a dynamic DNS service, but this can be unreliable, and could, in the right circumstances, mean that your mail is delivered to someone else, so it is not recommended!)
•You must have a permanent (or almost permanent) Internet connection. The sender will expect to be able to send you messages as necessary, so if you only connect to the Internet periodically, the chances of the sender trying to send their messages to you at the right times are low. It does not usually matter if your Internet connection may fail occasionally because the sender will usually hold onto messages they couldn't deliver immediately and periodically keep trying to send them over the next couple of days. The exact details of the retries are down to the sender, but this is the usual behaviour. Generally, if your router needs resetting and the Internet is down for a few minutes that won't cause any messages to be lost, but if your Internet connection is down for several days or is only up occasionally then you should not use incoming SMTP.
•You must be able to allow incoming TCP/IP connections on port 25 through your firewall/router, and your ISP must not block these connections.
These settings are mostly the default settings, so, in most cases, you will not need to make any setting changes.
•In Services -> SMTP Server -> General:
oYou must have the SMTP service bound to port 25 on an IP address which can be accessed from the Internet
oYou must have Do not require SMTP authentication for internal/incoming mail checked
oYou must have Check Client IP Address selected in the SMTP Anti-Relay Protection method
oYou must have Reject unrecognised local recipients checked
•You must create a DNS 'A' record pointing to the external IP address (usually your static IP address that your ISP provides you with) that your VPOP3 server will be receiving mail on. For instance, this could be mail.mycompany.com. The exact name doesn't matter, but it must be in a domain that you control and must not already be in use.
•For the domain(s) where you want messages to be sent, you must create a DNS 'MX' record referring to that domain, and with the MX record set to the name you set in the previous step. The MX priority doesn't generally matter.
The specifics of how you do this will vary from domain hosting company to domain hosting company, so we cannot specify the details here. It's a standard thing to do though, so most domain hosting companies will have instructions on how to do it. For instance:
If you have your domain's DNS hosted with us, then you can set it through your domain portal, or just ask us and we'll set it up for you.
Note that, in most cases, we recommend not setting multiple MX records for a single domain. It is generally a bad idea to set your ISP as the "backup MX server" for your domain. Doing this can cause strange problems with spam filtering and other spam reduction systems such as grey-listing, BATV checks etc.
You must configure your firewall/router to allow incoming connections on port 25 to your VPOP3 computer. This is usually called "Port forwarding". Again, because there are so many different firewalls & routers, we can't give you details of how to do it, but it is a very common requirement, so your router's documentation should have details. A site which may be useful is https://portforward.com which has instructions for many routers and firewalls.