diff --git a/dev/Sieve/Extensions/rfc5463.js b/dev/Sieve/Extensions/rfc5463.js
new file mode 100644
index 000000000..9c9123875
--- /dev/null
+++ b/dev/Sieve/Extensions/rfc5463.js
@@ -0,0 +1,64 @@
+/**
+ * https://tools.ietf.org/html/rfc5463
+ */
+
+import {
+	GrammarCommand,
+	GrammarTest,
+	GrammarString,
+	GrammarStringList
+} from 'Sieve/Grammar';
+
+/**
+ * https://datatracker.ietf.org/doc/html/rfc5463#section-4
+ */
+export class IHaveTest extends GrammarTest
+{
+	constructor()
+	{
+		super();
+		this.capabilities = new GrammarStringList;
+	}
+
+	get require() { return 'ihave'; }
+
+	toString()
+	{
+		return 'ihave ' + this.capabilities;
+	}
+
+	pushArguments(args)
+	{
+		let l = args.length;
+		if (args[l-1] instanceof GrammarString) {
+			this.method = args[l-1];
+		}
+	}
+}
+
+/**
+ * https://datatracker.ietf.org/doc/html/rfc5463#section-5
+ */
+export class ErrorCommand extends GrammarCommand
+{
+	constructor()
+	{
+		super();
+		this.message = new GrammarString;
+	}
+
+	get require() { return 'ihave'; }
+
+	toString()
+	{
+		return 'error ' + this.message + ';';
+	}
+
+	pushArguments(args)
+	{
+		let l = args.length;
+		if (args[l-1] instanceof GrammarString) {
+			this.method = args[l-1];
+		}
+	}
+}
diff --git a/dev/Sieve/Parser.js b/dev/Sieve/Parser.js
index 4a650b2ec..2ed9fdd3f 100644
--- a/dev/Sieve/Parser.js
+++ b/dev/Sieve/Parser.js
@@ -68,22 +68,10 @@ import {
 import { SpamTestTest, VirusTestTest } from 'Sieve/Extensions/rfc5235';
 import { DateTest, CurrentDateTest } from 'Sieve/Extensions/rfc5260';
 import { AddHeaderCommand, DeleteHeaderCommand } from 'Sieve/Extensions/rfc5293';
-
-import {
-	ErejectCommand,
-	RejectCommand
-} from 'Sieve/Extensions/rfc5429';
-
-import {
-	MailboxExistsTest,
-	MetadataTest,
-	MetadataExistsTest
-} from 'Sieve/Extensions/rfc5490';
-
-import {
-	IncludeCommand,
-	ReturnCommand
-} from 'Sieve/Extensions/rfc6609';
+import { ErejectCommand, RejectCommand } from 'Sieve/Extensions/rfc5429';
+import { IHaveTest, ErrorCommand } from 'Sieve/Extensions/rfc5463';
+import { MailboxExistsTest, MetadataTest, MetadataExistsTest } from 'Sieve/Extensions/rfc5490';
+import { IncludeCommand, ReturnCommand } from 'Sieve/Extensions/rfc6609';
 
 const
 	AllCommands = {
@@ -136,6 +124,9 @@ const
 		// rfc5429
 		ereject: ErejectCommand,
 		reject: RejectCommand,
+		// rfc5463
+		ihave: IHaveTest,
+		error: ErrorCommand,
 		// rfc5490
 		mailboxexists: MailboxExistsTest,
 		metadata: MetadataTest,
diff --git a/dev/Sieve/README.md b/dev/Sieve/README.md
index effb8ce32..0c24b4d3b 100644
--- a/dev/Sieve/README.md
+++ b/dev/Sieve/README.md
@@ -17,7 +17,7 @@ https://www.iana.org/assignments/sieve-extensions/sieve-extensions.xhtml
 - [x] RFC5293 editheader
 - [x] RFC5429 ereject / reject
 - [ ] RFC5435 enotify
-- [ ] RFC5463 ihave
+- [x] RFC5463 ihave
 - [x] RFC5490 mailbox / mboxmetadata / servermetadata
 - [ ] RFC5703 enclose / extracttext / foreverypart / mime / replace
 - [ ] RFC6131 vacation-seconds