MAPI vs. SMTP: Top 4 Differences You Should Know

1. Functionality

The MAPI open programming interface provides generic services that can be topped with customizations as users require. It has the functionality to fulfill the diverse requirements of messaging platforms, such as word processing, document sharing, workgroup creation, and diverse data storage. Essentially, MAPI provides comprehensive data storage and exchange functionalities and other unique features of its messaging system that can benefit application users.

MAPI also separates the programming interfaces for front-end messaging clients and back-end service providers. This gives single applications the ability to use several messaging systems and multiple applications to leverage a single service provider.

All MAPI components are compatible with a common user interface based on Microsoft Windows. Several systems are available for selection depending on user needs. Users can also work consistently with every selected system, which means MAPI functionality allows for absolute independence from specific messaging systems.

For instance, a messaging client can use MAPI to receive messages from voicemail, RSS feed, and fax. Messages will be received in a single “universal inbox” on arrival. An application handling all these systems reduces the costs associated with development, system administration, and user training.

Separating the client and provider interfaces removes programming dependencies placed on the messaging system by the application and vice versa. Client application devs and service providers can create code for a specific set of MAPI functionalities rather than several distinct messaging-specific or application-specific features. Developers can focus on their components (either service-side or client-side), and MAPI brings them all together, thus minimizing development costs and time.

The MAPI programming interface is feature-rich and aimed at streamlining workgroup applications, which are applications that communicate with various messaging systems like DEC All-In-1, voicemail, fax, and even public communications services like CompuServe, MCI MAIL, and AT&T Easylink Services. Service providers can be made available for all these systems over the MAPI interface.

Finally, MAPI supports cross-platform functionality for industry standards such as X.400 and SMTP. MAPI applications can run on older Windows versions, including 7, Vista, Server 2008, Server 2003, and Windows XP.

SMTP functionality begins with establishing an SMTP server, which allows email clients to connect with it for communication. Emails sent from users are transmitted from the email client over an SMTP connection to the server. This SMTP connection is built over the Transmission Control Protocol (TCP).

The SMTP client then uses commands to share instructions with the server and transfer data, such as the email addresses of the sender and the recipient and the contents of the email.

In the next step, the MTA (Message Transfer Agent or Mail Transfer Agent) checks whether both email addresses are from one email domain, such as yahoo.com. If the domains are common, the email is transmitted right away. If not, Domain Name System (DNS) is used by the server to identify the receiving domain, after which the email is sent to the correct server.

Basic SMTP commands — codes that power SMTP functionality such as email transmission between servers — are as follows:

1) HELO or EHLO (Hello): This command kicks off the email-sending process. It is used by the email client to identify itself with the SMTP server. The command is then sent back by the server, along with its domain name and IP address.

2) MAIL FROM: Once identification is completed, this command is used to specify the email sender. This code transmits the email address and notifies the SMTP server that a new transaction is being initiated. The server then resets everything in preparation for accepting the email address. The server will reply with a “250 OK” code if the email address is accepted successfully.

3) RCPT TO (Recipient To): This command identifies the email recipient once the 250 OK reply code is received. The SMTP server again responds with 250 OK, after which another RCPT TO command with a different receiver’s email address can be sent. This process repeats several times, depending on the number of email recipients.

4) DATA: This command is used to trigger the data transfer process between the client and the server. Once this command is executed, all email contents are transferred to the SMTP server, which replies using a “345” code. A single dot is sent in a line by itself after the message contents are transmitted to the server to notify it of the end of the message. If the server successfully accepts the message and prepares it for delivery, it sends another “250 OK” code to the sender client.

5) QUIT: Once the email is sent, the client sends this command to the SMTP server, closing the connection. If successful, the server replies with a “221” code.

6) RSET (Reset): This command is sent when the email transaction has to be stopped. While this command does not close the connection, it resets everything and flushes all previous data about the email and its sender and recipients. This command is used in case of an error, such as the entry of incorrect recipient information, post which the process must be restarted.

Finally, an SMTP Relay is defined as the process of transmitting emails between SMTP servers. It consists of the Mail Delivery Agent (MDA) and the MTA. It usually occurs when the sender and receiver have email addresses from different domains. SMTP Relay services increase email deliverability rates, helping users ensure outgoing messages reach the recipient’s inbox.

While “SMTP Host” refers to the server the email is sent over, the SMTP Relay is the process executed on that server.

2. Architecture

Because it is a client of the MAPI subsystem, the MAPI application is referred to as a client application.

The MAPI subsystem architecture consists of programming interfaces and a common user interface. The latter is a set of dialog boxes that helps establish a consistent look for client applications and a consistent user workflow.

The MAPI programming interface is leveraged by the MAPI subsystem, developers on the service provider side, and client-side software developers. It is the main object-based programming interface and is similar to the OLE Component Object Model.

The MAPI programming interface is used by messaging-based client applications written in C or C++ and the MAPI subsystem. This interface enables client software developers to make MAPI calls directly.

Messaging functionality can be implemented with either one MAPI client interface or a combination of interfaces. In the latter case, a single application can make calls to functions or methods belonging to any of the interfaces.

On the sender side, the UA creates the message and transfers it to the MTA. The MTA is then responsible for transferring the email content to the receiver MTA across the network.

Within the SMTP architecture, the client MTA is responsible for sending the email, while the server MTA is the component that receives emails.

The MTA uses TCP/IP to exchange messages between the sender and receiver.

It is responsible for queuing the pool of messages — in cases where the receiver is temporarily unavailable, the MTA schedules the messages for repeat delivery. The system administrator can configure the local MTA, removing the need for senders to manage it.

Once the MTA transmits the emails to the user’s local mailboxes, the UA can download them as required.

3. Applications

MAPI over HTTP is a transport protocol that enhances the stability and reliability of the connections between Outlook and Exchange. This is achieved by moving the transport layer to the HTTP model, an established industry standard.

This protocol enables higher visibility of transport errors and improved recoverability. An added feature is the support for an explicit pause-and-resume capability that allows supported clients to switch networks or resume from hibernation without foregoing the existing server context.

If users choose to implement MAPI over HTTP, they do not have to give up on using other protocols for Outlook to access Exchange. Outlook clients lacking MAPI over HTTP capability can still leverage Outlook Anywhere (RPC over HTTP) to connect with Exchange over a MAPI-enabled Client Access server.

Exchange 2016 and Exchange 2019 allow users to apply MAPI over HTTP either across the entire organization or to individual mailboxes.

MAPI over HTTP offers several benefits to supporting clients. For instance, it drives innovation in authentication by relying on an HTTP-based protocol.

Additionally, it supports quicker reconnection times in case of a communications break, as only TCP connections, not Remote Procedure Call (RPC) connections, would need to be rebuilt. Communication breaks may occur due to device hibernation or switching from wired to cellular or wireless networks.

Finally, MAPI over HTTP offers a session context that is connection independent. The session context is maintained by the server for a configurable period, even in cases where the user changes the network.

SMTP removes sending volume limits for users, which is especially helpful as many internet service providers (ISPs), web hosts, and email service providers limit the number of emails a user can send in a specific period. A dedicated SMTP allows users to send as many emails as required without limits.

Additionally, users can comprehensively monitor email delivery. Whether the email is delivered or not, SMTP allows users to receive helpful delivery information. For instance, users can monitor whether their messages were transmitted to the right recipient and analyze any arising error codes.

SMTP also allows users to maintain the privacy of their email lists. Using a private SMTP means email list data is not shared with any third party. This helps maintain the privacy of company and customer data.

However, it is worth noting that SMTP applications come with their own share of investment in terms of money, time, and effort. Operating an SMTP server needs a lot of resources, and users must constantly monitor and manage all operations. This can translate to having dedicated personnel for server setup and management. The costs of SMTP applications should be weighed against their benefits.

Unlike public cloud storage, SMTP servers operate locally. This has numerous advantages for specific use cases. However, it can also translate to vulnerability to internet issues or power outages. These operational challenges can be overcome by using backup servers and failsafe protections.

SMTP applications can be streamlined by adopting a third-party provider. Such service providers can configure SMTP to minimize email security and deliverability issues, even when contacting a large pool of recipients.

4. Advantages

Another benefit of MAPI is its capability to automatically retain a copy of sent emails, as all emails are routed through the sender’s outbox. This feature does not come in-built with SMTP, and users must either include themselves in the “BCC” field of their emails or program their servers specifically to retain copies of their sent emails.

Basically, for users of Outlook and Microsoft Exchange, MAPI is the more advantageous option as it was specifically developed to serve as a bridge between these two solutions.

Additionally, using MAPI over HTTP increases the efficiency of interactions with Exchange mailboxes as against Remote Procedure Calls (RPC).

Even though both MAPI and RPC are encapsulated within HTTP architecturally, users can reestablish connections with Exchange servers faster after network disruption when using MAPI over HTTP rather than Outlook Anywhere.

MAPI over HTTP also features more robust security when switching networks, such as from the enterprise network to a personal cellular network. In such cases, the server retains the active session as it was before the network was switched.

Personal networks are also more secure and reliable with MAPI over HTTP, especially for Outlook clients connecting to Exchange Server 2019.

Another key advantage of switching Outlook to MAPI over HTTP is an improved user experience and the faster delivery of emails across all types of connections. Swifter connection times to Exchange are a major reason for this advantage.

Finally, MAPI over HTTP boosts the reliability and stability of the connections between Outlook and Exchange by shifting the transport layer to the HTTP model. This makes it easier to spot transport errors, thereby enhancing recoverability.

MAPI was introduced as a Microsoft protocol for use with Outlook. As Outlook and Microsoft’s Exchange server gained popularity, more email clients adopted the protocol. However, SMTP is more popular as it has been around virtually since email was invented. Every major email client today is capable of supporting SMTP use. In fact, it is the default protocol in many cases.

Additionally, SMTP is client-agnostic, allowing users to switch clients without affecting functionality. This is not the case with MAPI, where users must make changes to the configuration if clients are switched, as the server would not automatically be able to detect the client change.

SMTP is especially popular among users of non-Microsoft email clients, such as Mozilla Thunderbird, wishing to connect to free email servers such as Google Gmail.

In many cases, users only have to enter their credentials, and they’re done.

Apart from this, SMTP offers back-end access to messages that explain error codes in case an email fails to be delivered.

Users can also set up SMTP servers to receive email statistics. This feature allows for generating statistical reports for click and open rates and other metrics.

Finally, SMTP systems can be synchronized at the server level to carry out bulk actions. For instance, a setup consisting of a hundred computers that all need synchronization with an SMTP server does not need each computer configured individually. Rather, users can execute synchronization at the server level, allowing them to manage all email accounts.