Can a Message have multiple senders?
email, imap, jakarta-mail, java
Solution
Yes, it seems that `Message.getFrom()` can really return multiple addresses.
I had a look at the sources for Apache Geronimo's implementation of the JavaMail API, and it will return multiple addresses if there are multiple `From:` headers, or multiple addresses inside one header.
As to whether this could happen:
As explained by Alex K.'s answer, the standard allows multiple "From" addresses if there is a single "Sender". I don't know whether anyone really sends mails with multiple "From" addresses, but it is standards-compliant.
Another situation which actually happens in practice:
Some spammers apparently send mail with multiple `From:` headers. This is not standards-compliant, but apparently some mail servers still accept the mail. This is apparently done to get past mail filters that filter by the `From:` address. The spammers include multiple addresses in the hope that a simple-minded filter will let the message pass if it finds one header with a "From"-address it likes.
So in summary: Yes, you should expect `Message.getFrom()` to return multiple addresses (or none at all). However, you probably don't need to expend a lot of energy for handling that case. Maybe you can even get away with just logging it as an error - that depends on your application.
Problem
When I want to check who send a specific email to me with JavaMail. I can use ``` Message.getFrom() ``` which returns an ``` Message[] ``` In what circumstances can a revived Message have multiple Identities it came from? Regarding the API this makes more sense for outgoing Emails. So can I really on, that: ``` Address from = message.getFrom()[0]; ``` Always gives me back exactly 1 Address which the Message was send from? I have now Implemented something like: ``` Address[] fromAddress = message.getFrom(); if (fromAddress == null || fromAddress.length > 1) { // Don't Process the Email and Notify me } ```