jstedfast/MailKit · error · ArgumentException

Annotation entry paths must not end with '/'.

Error message

Annotation entry paths must not end with '/'.

What it means

AnnotationEntry.ValidatePath rejects entry-name paths that end with a '/' character. IMAP annotation entries combine a part specifier, a path, and a scope suffix (e.g. /priv); a trailing slash would produce a malformed entry name. The library throws ArgumentException with nameof(path) as the parameter name.

Solutions

1. Remove the trailing '/' from the path string before constructing the AnnotationEntry
2. Trim trailing slashes: path = path.TrimEnd('/')
3. Verify the path you intend is an annotation entry name (e.g. "comment", "/vendor/cmu/token"), not a mailbox path

Example fix

// before
var entry = new AnnotationEntry ("/vendor/cmu/token/", AnnotationScope.Shared);
// after
var entry = new AnnotationEntry ("/vendor/cmu/token".TrimEnd ('/'), AnnotationScope.Shared);

if (string.IsNullOrEmpty (path))
    throw new ArgumentException ("Path is required.");
if (path.EndsWith ("/"))
    throw new ArgumentException ($"Path '{path}' must not end with '/'.");

bool IsValidPath (string? path) =>
    !string.IsNullOrEmpty (path) && !path.EndsWith ("/") && !path.EndsWith (".");

try {
    var entry = new AnnotationEntry (path, scope);
} catch (ArgumentException ex) when (ex.ParamName == "path") {
    logger.LogError (ex, "Invalid annotation path: {Path}", path);
}

When it happens

Trigger: Calling the AnnotationEntry constructor or a factory that takes a path with a string such as "/vendor/cmu" or "comment/" — i.e. path[path.Length-1] == '/'.

Common situations: Building entry paths programmatically with string concatenation (e.g. Path.Combine or trimming/prefix joins) that accidentally leaves a trailing slash; copying IMAP mailbox-style paths that conventionally end in a hierarchy delimiter.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Annotation entry paths must not end with '.'.
• Invalid part-specifier.
• Value cannot be null. (Parameter 'entry')
• Value cannot be null. (Parameter 'partSpecifier')
• Value cannot be null. (Parameter 'part')

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/fb2d60036781b05b. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/AnnotationEntry.cs:149

			for (int i = 1; i < path.Length; i++) {
				char c = path[i];

				if (c > 127)
					throw new ArgumentException ($"Invalid character in annotation entry path: '{c}'.", nameof (path));

				if (c >= '0' && c <= '9' && pc == '/')
					throw new ArgumentException ("Invalid annotation entry path.", nameof (path));

				if ((pc == '/' || pc == '.') && (c == '/' || c == '.'))
					throw new ArgumentException ("Invalid annotation entry path.", nameof (path));

				pc = c;
			}

			int endIndex = path.Length - 1;

			if (path[endIndex] == '/')
				throw new ArgumentException ("Annotation entry paths must not end with '/'.", nameof (path));

			if (path[endIndex] == '.')
				throw new ArgumentException ("Annotation entry paths must not end with '.'.", nameof (path));
		}

		static void ValidatePartSpecifier (string partSpecifier)
		{
			if (partSpecifier == null)
				throw new ArgumentNullException (nameof (partSpecifier));

			char pc = '\0';

			for (int i = 0; i < partSpecifier.Length; i++) {
				char c = partSpecifier[i];

				if (!((c >= '0' && c <= '9') || c == '.') || (c == '.' && (pc == '.' || pc == '\0')))
					throw new ArgumentException ("Invalid part-specifier.", nameof (partSpecifier));

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