Why was my e-mail to someone at Physics bounced?

Before proceeding, you should look at the bounce/reject message you received and find the reason listed. Unless your mail server strips out error messages, you will find a message from our server listing the cause of the rejection. When you have found that, look below to find the corresponding explanation (if the rejection message itself is not clear enough).

451 Your e-mail server xxxxx is blacklisted in xxxxxxx. Please inform your e-mail service provider. http://xxxxxxxxx

Your outgoing e-mail server is blacklisted (usually for being a known originator of spam or for allowing spammers to relay mail through the server). At the end of that error message is a URL explaining why and what to do. You, if you run your own servers, or your e-mail provider will need to clear this up. While it is blacklisted, we cannot accept mail from this server. You may try another route such as using another e-mail account or another outgoing e-mail server.

Inconsistent PTR and A DNS records for xxx.xxx.xxx.xxx, please inform your email service provider.

This is a particularly troublesome error as it should never happen for properly configured servers. We should only see this error from spambots and the like, but far too often we see it from legitimate senders. In brief, the DNS record for the sending server was not set up properly and must be fixed by whomever controls the DNS for the server(s). Usually your IT staff or ISP (Verizon, Comcast, etc.).

A denial response is sent back identifying the problem. If your ISP/provider does not understand, here are the 'rules' (RFCs) that outline this that all providers are expected to abide by:

RFC 1912 Section 2.1 states "Every Internet-reachable host should have a name" and "Make sure your PTR and A records match".

RFC 1033 Section "INSTRUCTIONS" states the following (note especially the last sentence):
Adding a host.
To add a new host to your zone files:
Edit the appropriate zone file for the domain the host is in.
Add an entry for each address of the host.
Optionally add CNAME, HINFO, WKS, and MX records.
Add the reverse IN-ADDR entry for each host address in the appropriate zone files for each network the host is on.

550 Attachment with .eml extension is not allowed

As this sort of attachment is a favorite vector for spammers and malware writers, and as the .eml file as a file type specific to the mail program sending it and not a part of standard e-mail conventions, our general rule is to reject messages containing .eml attachments.

Please try sending your message again without the attached .eml file. If you are forwarding a message and this is the default behavior of your e-mail program, you can remedy this by changing the behavior to "forward inline" instead of "forward as attachment". Consult your IT personnel for instructions or type the name of your e-mail program and "forward inline" into your preferred search engine.

To change this behavior: In Thunderbird, this setting is under Preferences -> Composition.

PLEASE NOTE: If you are forwarding a spam/scam/phishing e-mail, don't be surprised if your message is rejected. As you can imagine, passing around such messages does more harm than good. If you feel the need to inform others of a scam, send them details of it, but not the actually scam itself (or you may find your e-mails ending up in their junk folder as well as the spam. The mail server can't judge your intention, only the content.).

Mailbox not found (or No such user)

Quite literally, the address that the mail is addressed to does not exist. Check for spelling errors or extraneous characters in the e-mail address you are trying to send to. Senders: Using "noreply@yourdom.ain" or some other fictitious address may be a simple way to avoid getting any unwanted replies, but it's not a valid address and receivers have every right to reject e-mail from fake addresses such as this. To truly fight spam, we all need to play by the rules. If you send mail from a non-existent address, you cannot and should not assume that it will be delivered to the intended recipient.

Quota Exceeded (or 'inbox lockfile' errors)

The person you are attempting to e-mail has filled up their disk quota and cannot receive any more e-mail. This is unlikely to happen for Physics accounts, but will often happen to FAS accounts and Physics accounts that are forwarded somewhere else. There is little you can do until the person reduces their disk usage enough for new mail to be delievered.