jstedfast/MailKit · error · ArgumentException

Cannot sort using an empty query.

Error message

Cannot sort using an empty query.

What it means

MailKit throws this ArgumentException from ImapFolder.Sort when the supplied IMAP search-program string is empty after trimming. An empty query would produce a malformed UID SORT command that no server can evaluate, so the library validates it locally before sending.

Solutions

1. Build a valid IMAP search program string (e.g. "ALL" matches everything, or "SINCE 1-Jan-2024") before calling Sort.
2. Guard the call: trim and check query.Length > 0, or throw/return early with a meaningful application-level error.
3. Prefer the SearchQuery object-based Sort overloads to avoid hand-built query strings entirely.

Example fix

// before
folder.Sort (orderBy, userQuery); // userQuery may be ""

// after
if (string.IsNullOrWhiteSpace (userQuery))
    userQuery = "ALL";
folder.Sort (orderBy, userQuery);

query = query?.Trim ();
if (string.IsNullOrEmpty (query))
    query = "ALL"; // or reject at the application layer
folder.Sort (orderBy, query);

try {
    ids = folder.Sort (orderBy, query);
} catch (ArgumentException ex) when (ex.Message.Contains ("empty query")) {
    ids = folder.GetUids (fallbackOrder: orderBy); // app-level fallback
}

When it happens

Trigger: Calling folder.Sort(orderBy, "") or folder.Sort(orderBy, " ") with a whitespace-only search program string; building the query string dynamically and getting an empty result.

Common situations: String-concatenating search criteria from user input where no criteria were selected; stripping out an invalid term and leaving nothing; passing the wrong variable (empty instead of the built query).

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• No sort order provided.
• Annotation attribute specifiers cannot be empty.
• Annotation entry paths cannot be empty.
• The host name cannot be empty.
• The SearchOptions.All flag cannot be combined with a…

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/616605c81c1bd0c6. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Net/Imap/ImapFolderSearch.cs:1399

		/// The server replied with a NO or BAD response.
		/// </exception>
		public override Task<SearchResults> SearchAsync (SearchOptions options, SearchQuery query, PartialRange partialRange, CancellationToken cancellationToken = default)
		{
			if ((options & SearchOptions.All) != 0)
				throw new ArgumentException ("The SearchOptions.All flag cannot be combined with a partial range.", nameof (options));

			return SearchAsync (options, query, partialRange, true, cancellationToken);
		}

		ImapCommand QueueSortCommand (string query, CancellationToken cancellationToken)
		{
			if (query == null)
				throw new ArgumentNullException (nameof (query));

			query = query.Trim ();

			if (query.Length == 0)
				throw new ArgumentException ("Cannot sort using an empty query.", nameof (query));

			if ((Engine.Capabilities & ImapCapabilities.Sort) == 0)
				throw new NotSupportedException ("The IMAP server does not support the SORT extension.");

			CheckState (true, false);

			var command = "UID SORT " + query + "\r\n";
			var ic = new ImapCommand (Engine, cancellationToken, this, command);
			if ((Engine.Capabilities & ImapCapabilities.ESort) != 0)
				ic.RegisterUntaggedHandler ("ESEARCH", UntaggedESearchHandler);
			ic.RegisterUntaggedHandler ("SORT", UntaggedSearchHandler);
			ic.UserData = new SearchResults (UidValidity);

			Engine.QueueCommand (ic);

			return ic;
		}

View on GitHub (pinned to 9d3859a785)