jstedfast/MailKit · error · ArgumentException

No sort order provided.

Error message

No sort order provided.

What it means

MailKit throws this ArgumentException from the SearchQuery-based ImapFolder.Sort overload when the orderBy list is null-checked earlier and then found empty. A UID SORT command requires at least one sort criterion; an empty list would yield an invalid command, so the library rejects it before touching the network.

Solutions

1. Ensure orderBy contains at least one OrderBy entry (e.g. OrderBy.Date with SortOrder.Descending) before calling Sort.
2. Default to a sensible ordering (like reverse chronological) when the list is empty.
3. Validate at the configuration/UI layer that at least one sort key is always selected.

Example fix

// before
folder.Sort (orderBy, query); // orderBy may be empty

// after
if (orderBy.Count == 0)
    orderBy.Add (new OrderBy (OrderByItem.Date, SortOrder.Descending));
folder.Sort (orderBy, query);

if (orderBy == null || orderBy.Count == 0)
    orderBy = new List<OrderBy> { new OrderBy (OrderByItem.Date, SortOrder.Descending) };
folder.Sort (orderBy, query);

try {
    ids = folder.Sort (orderBy, query);
} catch (ArgumentException ex) when (ex.Message.Contains ("No sort order")) {
    ids = folder.Sort (DefaultSortOrder, query);
}

When it happens

Trigger: Calling folder.Sort(new List<OrderBy>(), query) or passing an OrderBy collection that was built conditionally and ended up empty; also the async equivalent.

Common situations: User-configurable sort preferences where the user deselected all sort fields; deserializing sort settings from config/JSON that produced an empty list.

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

• Cannot sort using an empty query.
• The SearchOptions.All flag cannot be combined with a…
• The IMAP server does not support the SORT extension.
• The IMAP server does not support the ESORT extension.
• No indexes were specified.

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/0b12e1a52c294c17. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Net/Imap/ImapFolderSearch.cs:1544

		public virtual async Task<SearchResults> SortAsync (string query, CancellationToken cancellationToken = default)
		{
			var ic = QueueSortCommand (query, cancellationToken);

			await Engine.RunAsync (ic).ConfigureAwait (false);

			return ProcessSortResponse (ic);
		}

		ImapCommand QueueSortCommand (SearchQuery query, IList<OrderBy> orderBy, CancellationToken cancellationToken, out string? charset)
		{
			if (query == null)
				throw new ArgumentNullException (nameof (query));

			if (orderBy == null)
				throw new ArgumentNullException (nameof (orderBy));

			if (orderBy.Count == 0)
				throw new ArgumentException ("No sort order provided.", nameof (orderBy));

			CheckState (true, false);

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

			var args = new List<object> ();
			var optimized = query.Optimize (new ImapSearchQueryOptimizer ());
			var expr = BuildQueryExpression (optimized, args, out charset);
			var order = BuildSortOrder (orderBy);
			var command = new StringBuilder ("UID SORT ");

			if ((Engine.Capabilities & ImapCapabilities.ESort) != 0)
				command.Append ("RETURN (ALL) ");

			command.Append (order);
			command.Append (' ');
			command.Append (charset ?? "US-ASCII");

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