| XMPP | Extensible Messaging and Presence Protocol |
| IMPP | Instant Messaging and Presence Protocol |
| CPIM | Common Presence and Instant Messaging |
| SIMPLE | SIP for Instant Messaging and Presence Leveraging Extensions |
| EAP | Extensible Authentication Protocol |
| EAPOL | Extensible Authentication Protocol Over LAN |
| EAPOE | Extensible Authentication Protocol Over Ethernet |
| PEAP | Protected Extensible Authentication Protocol |
| LEAP | Lightweight Extensible Authentication Protocol |
| IMP | Instant Messaging Protocol |
| BEEP | Blocks Extensible Exchange Protocol [engl.] Firmenbezeichnung |
| NAMP | NetWare Asynchronous Messaging Protocol |
| NIMP | NetWare Internetwork Messaging Protocol |
| P2 | Interpersonal Messaging Protocol [for heading and body] |
| SMP | Standby Monitor Presence |
| IPP | Internet Presence Provider |
| SPD | Serial Presence Detect |
| PPC | Physical Presence Command |
| POP | Point of Presence / Purchase |
| EVE | Extensible VAX Editor |
| ESE | Extensible Storage Engine |
| ELF | Extensible Linking Format |
| XSL | Extensible Stylesheet Language |
| XML | Extensible Markup Language |
| XLL | Extensible Linking Language |
| XVT | Extensible Virtual Toolkit |
| XHTML | Extensible Hypertext Markup Language |
| XFDL | Extensible Forms Description Language |
| NeWS | Networked Extensible Windowing System |
| XSLT | Extensible Stylesheet Language Transformation |
| XBRL | Extensible Business Report Language |
| SEEM | Simple Efficient Extensible Mesh |
| XAML | Extensible Application Markup Language |
| UM | Unified Messaging |
| XUL | Extensible / XML-Based User Interface Language |
| XSLFO | Extensible Stylesheet Language Formatting Object |
| ERMES | European Messaging System |
| SPIM | Spam over Instant Messaging |
| MQI | Messaging and Queuing Interface |
| MMB | Medium Messaging Benchmark |
| EMS | Enhanced Messaging Service |
| UMS | Unified Messaging Server |
| NGM | Netware Global Messaging |
| JMS | Java Messaging Service |
| OMI | Open Messaging Interface |
| UMS | Unified Messaging System |
| VIM | Vendor Independent Messaging |
| MT | Mobile Terminated [Messaging] |
| SMC | Secure Messaging Card |
| EEMA | European Electronic Messaging Association |