End-users can access their mailboxes via web clients or desktop email clients such as Outlook / Outlook Express / Thunderbird etc. When configuring a desktop email client to check the incoming mail, the connection to the server can be an IMAP or a POP connection.

Organizations need to decide on a mail access policy depending on a number of factors such as the messaging server architecture, available bandwidth on the connections from the user’s desktop to the server, mail archiving policies, etc. The following paragraphs will help administrators decide on a suitable policy for individual users. System administrators can define a global policy or define different policies for individual users/groups of users.

POP access from a desktop email client

When to use POP access

  • The organization has a consolidated mail server setup accessed via remote branches over corporate WAN.
  • Individual mail stores are large.
  • There is insufficient storage capacity on the central servers.
  • Users have independent workstations.

When NOT to use POP access

  • If using clients with the “Leave a copy” turned on, the client may download duplicate mails, if the server is switched to another one in the back end or if the mail store is made blank temporarily. Any change on the backend causes the indexes and other tables on the POP client to get disturbed causing duplicate mails to get downloaded. If you must use POP, please don’t leave a copy on the server

Advantages

  • Lower bandwidth usage on corporate WAN
  • Lower storage requirements on central servers

Limitations

  • Can only archive the incoming mail for an individual user. No central archiving for the entire mailbox as mail in sent mail and other folders not available on the central servers.
  • Maintaining an individual mailbox is end-users' responsibility.
  • Cannot access the entire mailbox from any other device/mail client connected to the server.
  • If users leave a copy on the server and as the mailbox on the server grows, the response of the POP server reduces drastically after it crosses a threshold and also negatively impacts the server I/O thereby creating a side effect of reduced performance of the entire server.
  • If you are using MS Outlook clients, and accessing your POP server with the “Leave a copy” option turned on, you are likely to get duplicate mail in case the server is migrated to a new hardware/VM or even if the storage is swapped.

IMAP access from a desktop email client

When to use IMAP access

  • The organization has a distributed mail server setup with end users accessing the local mail server
  • If the mail servers are centralized, then adequate bandwidth from a branch to the central servers is available
  • Quota restrictions are applied on individual mailboxes.
  • There is sufficient storage capacity on the central servers
  • There are independent workstations for all the users

When NOT to use IMAP access

  • If there is any change on the backend like a server crash and subsequent migration to another server, or if storage is replaced with a new blank mail store, the IMAP indexes etc on the client, get all mixed up and the client has to resync the entire mail store. In such a situation it is best to not use the IMAP client and instead switch to using only the web client of the mailbox.

Advantages

  • Central mail stores for individual users, which can be archived and checked for compliance by the administrators
  • Central mail stores that can be accessed via different devices connecting to the central server. Mirror access.\
  • Once the initial sync is done, the response to checking for new mail and downloading mail is even better than POP. also the load on the server stays more or less uniform even if the mailbox grows to a large size.

Limitations

  • In case of a central server setup, higher bandwidth utilization on the corporate WAN.
  • For offline access, the client must support caching
  • Large storage capacity at the central mail servers
  • High volume high-speed backup solution for the large mail store
  • If the IMAP store is temporarily made blank on the mail server, the IMAP client is likely to think that it's a much-shrunk account and change its folder subscriptions, and indexes according to the new server mail store. This can happen in case of a disaster recovery situation where the server is switched to a new one with a blank mail store and then the old mail re restored from a backup.

Webmail access using a browser

When to use webmail access

  • The organization has a distributed mail server setup with end users accessing the local mail server
  • If the mail servers are centralized, then adequate bandwidth from a branch to the central servers is available
  • There are quota restrictions on individual mailboxes
  • Sufficient storage capacity on the central servers is available.
  • Users do not have independent workstations or are mostly on the move.
  • In case of a disaster on the backend where a blank mail store is made active temporarily to get access to the new mail only, it is best to avoid using POP/IMAP and use only the Baya client.

Advantages

  • Central mail stores for individual users, which can be archived and checked for compliance by the administrators.
  • Central mail stores that can be accessed via different devices connecting to the central server
  • Lower administrative costs of configuring desktop email clients.
  • Users can access their mailboxes from any PC connected to the mail server. Works well when different users in different shifts use the same infrastructure. For example in a BPO

Limitations

  • In case of a central server setup, higher bandwidth utilization on the corporate WAN
  • Large storage capacity at the central mail servers
  • High volume high speed backup solution for the large mail store.
  • Servers need more computing power