In your case, it’s fairly clear: the message was probably delivered to the other three recipients.
In the general case, of course, things are never quite that simple.
Things also get more complicated because you’re not even guaranteed to get a bounce-back message if something goes wrong.
I’ll examine the possibilities.
The path email takes
Email makes several stops along its path from you to your recipients, and, of course, an error can happen at any point along that path.
Exactly what an error means depends on at least two things:
- Where along the path it happened.
- The specific error.
The key in every case is to carefully read the error message for clues as to what broke and where.
Let’s look at a few examples.
Failures before email leaves
Some errors are generated by your email program when you press the Send button. These types of errors include anything that can be detected before sending, including a malformed email address, improper account configuration, or a misbehaving mail server.
In these cases, the mail never left your machine, and hence wouldn’t make it to any recipients.
Some email programs create their own “bounce” messages in this scenario. Rather than popping up an error message immediately, they manufacture a faux-bounce in the form of an email message placed in your inbox.
Failure getting to your mail sever
By “your mail server” I mean the mail server your email program contacts when sending mail. Typically, that’s the “SMTP” server setting, and the configuration information will have been provided to you by your email service or ISP.
The three most common causes of failure when sending email at this stage are:
- Bad account information, such as a bad username or password.
- Bad account configuration, such as a bad mail server name, port, or security requirements.
- Something about the message itself, such as some kind of early spam detection or size limits of some sort.
Regardless of whether it comes to you as an immediate popup or a bounce, the error message will tell you exactly what’s wrong. Read it carefully.
Failures at this stage prevent all copies of the email from being sent; the message still hasn’t left your machine.
Failures en route
Your mail server is responsible for taking the single message you’ve sent and sending it one at a time to each recipient. Errors at this point fall into two general buckets:
- Your email server can’t contact the recipient’s email server.
- The recipient’s email server refuses to take delivery of the message.
In the first case, you’ll usually get a bounce from your email server telling you it was unable to contact the remote server. The bounce message will come “From:” your mail server. Depending on the error, you can get the response immediately, or it can take several days for the mail server to give up.
In the second case, the bounce message may come either from your mail server or from the recipient’s mail server. In either case, the reason will be included in the message. Common problems include:
- The recipient’s mail server thinks your email is spam.
- The recipient’s mailbox is full (or “over quota”) and cannot accept any more mail until it’s cleaned out.
- The recipient’s email account has been closed and no longer accepts mail.
- You’ve typed the recipient’s email address in wrong.
Regardless of the reason, if the email has reached this point, each failure is per-recipient, meaning some of the emails will make it, and others — the ones that result in an error message back to you — will not. The key here is that the error message will specifically reference one of the email addresses you attempted to send to. It’s that address that has the problem.
Confusing bounce messages
Bounce messages can be confusing. There’s often a lot of technical gobbledygook making the message difficult to understand.
Please take the time to read it anyway. Quite often, the error will be buried within that mess: brush the mess aside and the reason for the failure becomes clear.
Unfortunately, sometimes bounce messages are the equivalent of “It didn’t work”, with no additional information as to why it didn’t work. When that happens, the best you can do is to use the information in the “From:” line of that message to see which server along the sending path generated the error. Use the information above to make an educated guess as to what might have gone wrong, and whether it’s something you can fix.
Missing bounce messages
Finally, it’s possible you won’t get a bounce message at all, and your email will not be delivered.
The problem is spam. Since so much spam is sent to invalid or blocked email addresses, the load of sending bounce messages for every such message can become overwhelming. As a result, many email services elect not to send them at all.
There’s little you can do when this happens. If you suspect your email hasn’t made it through, about all you can do is ask your recipient — using a media different than email!