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Reading Helix Mail with the IMAP Protocol

Helix mail can be read with mail clients like Thunderbird and Windows Live Mail using two possible protocols: POP and IMAP. We recommend the IMAP protocol, but you should consider the pros and cons below while making your decision.

Advantages of IMAP

IMAP keeps all mail on the server (i.e. Helix). Mail is not automatically downloaded to your desktop machine each time you connect, although you can still explicitly choose to save messages locally. This has the following advantages:

  • IMAP is much faster than POP
  • IMAP downloads messages one at a time; POP downloads all new messages each time a connection is made
  • Mail can be accessed consistently from multiple clients (e.g. home, office); all changes you make to your mail folders (deleting messages, moving into folders) will be 'seen' from any client
  • Mail can be accessed simultaneously from multiple clients (some sessions may become read-only)
  • A misconfigured IMAP client is a nuisance; a misconfigured POP client can cause serious problems that are difficult and time-consuming to recover from
  • IMAP is immune to "duplicate messages" that occasionally afflict POP clients

Possible disadvantages of IMAP

  • If you have been downloading all your mail to your local desktop machine through Eudora/POP, when you switch to IMAP this local mail will no longer be visible. It is possible to upload the Eudora .mbx files to Helix and access them as remote folders through IMAP. Please contact the Helix Staff (staff@helix.nih.gov) if you need help with this.
  • A message has to be explicitly saved to your desktop machine if you want to use it locally (for instance, if you want to include parts of a large mail message into a document).
  • Mail has to be explicitly saved on your laptop or desktop if you want to work on it offline.

Mailbox size

In order to manage system resources fairly, there is currently a 1 GB Inbox size limit. There are no limits on the number or size of mail folders you create through IMAP; folders reside on Helix in your mail directory. You also have the option of saving messages locally on your desktop machine.

When your Inbox exceeds 1 GB you will receive a warning message. If your Inbox remains larger than 1 GB for 21 days it will be automatically compressed and moved to a mail corral directory; initially no mail messages will be deleted or lost, but the corralled mail will be deleted in another 3 months.


Travelers and other users who are connecting from outside NIH can also use the secure SquirrelMail web mail service at http://helix.nih.gov/mail to access Helix mail. SquirrelMail is basically a preconfigured IMAP client on Helix. Your browser will need to have cookies enabled.

Detailed instructions for configuring IMAP on:

Microsoft Outlook 2010
Microsoft Outlook 2003
Microsoft Live Mail
Outlook Express
Mozilla Thunderbird
PC Alpine
Mac Mail

Other IMAP clients are listed at: http://www.ii.com/internet/messaging/imap/isps/#toolsIMAP

Dial-In and Roaming Users

If connecting through a non-NIH Internet services provider (ISP), you will be unable to use an NIH host as an SMTP server. Instead, designate your ISP's outbound mail server as the SMTP server. The IMAP server and return address should remain helix.nih.gov

While traveling, we recommend the use of SquirrelMail (http://helix.nih.gov/mail). However, you can also choose to use your usual client; but you will not be able to send mail out through an NIH host. Instead, you will need to designate an SMTP (outbound mail) server at your current location. If traveling with your own laptop, you should only need to change the SMTP server as you move from site to site. You will have to ask a local system or network administrator for the server name to use.

Directory Services

NIH E-Mail Directory data is accessible via LDAP, a lookup protocol that is supported by an increasing number of mail clients. To configure such a client, specify directory.nih.gov as the LDAP server and o=nih,c=us as the search root.


You may encounter messages with a Subject header reading DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA. This pseudo-message is an Internet standard bookkeeping device used by IMAP and by the Pine mail program on Helix. These programs suppress the display of pseudo-messages, but other programs may not. The full story is available in the Pine Frequently Asked Questions document. The bottom line is that this is merely an annoyance, and deleting a pseudo-message is harmless.