Is it really possible to send email without connecting to a mail server? Not really.
When people ask "Do you support sending email without a mail server"? what they’re really asking is: "I don’t have an SMTP server, and I want to send email. I see other components available where it’s not necessary to specify an SMTP server. Does your component have that ability?" In short, the answer is Yes. But you need to understand some things before you jump in…
Here’s what happens inside those other components that claim to not need a mail server: The component does a DNS MX lookup using the intended recipient’s email address to find the mail server (i.e. SMTP server) for that domain. It then connects to that server and delivers the email. You’re still connecting to an SMTP server — just not YOUR server.
Chilkat provides an MxLookup method where you can lookup the SMTP hostname that services any given email address. You would then assign the SmtpHost property to this value. Chilkat can then connect directly to the recipient’s mail server and deliver the email.
There are a few gotcha’s though…
First, if you’re writing an application that is widely distributed, your app might be running within a network that blocks outgoing connections to the SMTP port. Earthlink, for example, is one major ISP that does this. When you are connected to the Internet via Earthlink, your apps can *only* connect to Earthlink’s SMTP server and will not be able to reach any remote servers. To send email, you must use Earthlink’s SMTP as a relay. This is common with ISPs. So… if your application is coded as in this example, it will not work within those networks.
Second, some SMTP servers will reject unauthenticated sessions attempting to send email from dynamic IP addresses. You may see this error in your LastErrorText:
553-Your attempt to send email to us has been blocked
553-because your email server is not currently on that domain’s Accepted
553-Senders list. To request addition to their Accepted Senders list,
553-please navigate with a Web browser to the following URL:
553 See http://www.dnsbl.us.sorbs.net/ (dul)
In a nutshell, just because you were able to do the MxLookup and connect to the recipient’s mail server, doesn’t mean you’ll be able to send email — it depends on the IP address from which you’re connecting.
Finally, the DNS lookup is potentially time consuming. In addition, you cannot use somebody else’s email server as a relay, so if you’re connecting to smtp.xyz.com, you can only send email to email addresses at xyz.com. To send email to 3 recipients at different domains means making 3 separate connections to 3 separate SMTP servers to send the email one at a time.