Email Inbox Quota, Message Size and Attachment Formats
Email Inbox Quota
IMSS does not currently have a quota on email inboxes or on the folders stored on our IMAP servers. However, we reserve the right to impose them on stored folders in the future if necessary. IMSS will never impose an inbox quota that will cause mail to be rejected.
However, the more messages that are stored in a mail folder, the more time it takes to retrieve that folder, so keeping the number of messages in your inbox small will make your email-reading experience more pleasant. This is especially true if you are using the POP protocol (that is, if you are getting your mail from pop-server.its.caltech.edu).
Most programs that use the POP protocol have a feature that allows you to set the number of days email is retained on the server. We strongly suggest, if you use POP and are leaving mail on the server, to set this to the smallest amount that will satisfy your needs, and to move incoming mail to local folders as soon as possible. If you find yourself leaving mail on the server because you need to access it from more than one computer, we strongly suggest you switch to using the IMAP protocol, which is explicitly designed to support reading mail from multiple computers.
We also suggest, if you use POP, that you activate any features similar to "delete mail from server when it is deleted from the local computer". This will help prevent you from seeing mail again that you have already seen and deleted if you look at it with another computer or email program.
Message Size Limits
The IMSS SMTP servers are configured to bounce any messages they receive that are larger than 20 megabytes. Any attempt to send a message to an address "@caltech.edu" or "@its.caltech.edu" that is larger than that will fail (as will an attempt to send such a message to an address for one of the other mail domains we manage, such as "@cco.caltech.edu").
We have this limit in place for two reasons:
- Many email programs have a hard time with very large email messages or very large mailbox files. In the past, when we did not limit the incoming message size, many people would find it was impossible for them to read their mail due to one or a few too-large messages in their mailbox.
- Processing large email messages puts more strain on the SMTP servers, especially if they are mailed to a large number of people at once. The latter situation can bog down the entire mail system, negatively affecting everyone whose mail is sent to our systems.
Our current limit is based on an informal survey we conducted of other technical institutes and universities; the majority of the locations we contacted had a limit around 25 megabytes.
We understand that email is a convenient way to transfer files between people, but we have to place restrictions on it to maintain an adequate level of service for everyone.
If you need to send large files to people, we suggest you to get an IMSS account, if you don't have one, and place the file in the web space that is available to you as a result. Your correspondents can then retrieve your files using a web browser. If you need help doing this, contact the IMSS Help Desk by calling x3500 or emailing help@caltech.edu.
File Attachments and Formats
If you want to send someone else a file through email, a convenient way to do that is to "attach" it to an email message. Your email program converts the email message and the file or files into a special encoded form that mail servers can process. Your recipient's email program then decodes the attachment and lets them either save it or view it with an appropriate program (such as Microsoft Word if you are sending a Word document).
Most mail programs use the MIME standard to encode attachments. Macintosh computers also use the binhex standard, and on rare occasions you may see messages from Unix computers encoded with the uuencode standard.
Sending a message with an attachment
Most mail programs support mail attachments. The type of encoding that is used, however, varies. Some mail programs may only support one type of message encoding, while others may give you a choice. In any case, you should not automatically assume that the recipient of your message will be able to decode your message attachment. If at all possible, check with the recipient beforehand to find out what types of attachments their mail program supports. Failure to do so may result in frustration on their part and yours as they try to determine what to do with an attachment that they cannot easily read.
Sending large attachments
The short answer is, don't! It is generally not a good idea to send large email messages. A lot of mail handlers will not cope with messages larger than a few MB in size. If they don't have enough space to deal with it, your message will likely be returned to you. Your message may need to pass through several mail handlers before it reaches its final destination.
Be aware that if you send a very large message, the recipient may not be able to accept it or their e-mail client may have trouble downloading the message. Therefore we suggest you send a follow-up message in order to get confirmation of delivery
If you do need to send a large file to another user, try using dropbox.caltech.edu.
A note on HTML email
Many email programs give you an option to send your email in both plain text and HTML, or in HTML only. IMSS recommends against using such an option, and suggests activating any option for sending email in plain text only. Email in both formats or in HTML only is quite inconvenient for the substantial number of email readers who use a mail program that does not automatically render HTML into readable text. (Many people turn off the HTML rendering to avoid computer viruses that spread by exploiting security problems in the HTML rendering.) It also causes even the simplest text message to balloon to an unreasonably large size.
Receiving a message with an attachment
If you haven't received a message with an attachment yet, don't worry, you will. Will you be able to decode and view the message attachment with your mail program? Well, that depends.
IMAP and POP Clients
Some Windows and Macintosh mail clients (such as Outlook, Eudora, Netscape Mail, etc.) have built-in support for the three major methods of encoding for message attachments. With these programs, it's relatively easy to view message attachments. The decoding of the attachment into its original form occurs behind the scenes. If you have an application installed that can view the original file type, you may see an icon in the message window which, when clicked, will launch the application and open the file attachment. (In Windows, you may need to define the application to launch based on the filename's three-letter extension).
If your Windows or Macintosh mail program is not able to automatically decode the message attachment, then you will need to try to decode the attachment manually, or ask the sender to send it again using a different encoding method.
Unix Clients
Some programs can decode mime messages automatically, such as Pine or Mutt.
Alternately, try saving the message to a file.
Then do:
metamail < message-file
metamail should give you several options, including unpacking and saving the JPG file if you are not at a console which can display it.
After this, you will be able to deal with the file with standard tools to deal with JPG files (programs such as xv to display and convert into other file formats, or the 'pbm' tools).
