jstedfast/MailKit · error · NotSupportedException

The folder does not support partial searches.

Error message

The folder does not support partial searches.

What it means

MailFolder's base-class Search overload that takes a PartialRange is a virtual placeholder that is only implemented by servers/folders supporting partial range search (e.g. IMAP with the ESEARCH extension). The base MailFolder implementation throws NotSupportedException to signal that this folder type does not support searching a subset/range of results. Callers must use the non-partial Search overloads or connect via an IMAP folder that supports partial search.

Solutions

1. Use the non-partial Search(SearchQuery) / Search(SearchOptions, SearchQuery) overloads and take/skip results client-side instead of a PartialRange.
2. Ensure the folder is an ImapFolder connected to a server supporting partial search results (check folder/support capabilities) before calling the PartialRange overload.
3. If partial results are needed for pagination, fetch a range of UIDs/messummary objects instead of relying on partial search.

Example fix

// before
var results = folder.Search(SearchOptions.None, query, new PartialRange(0, 10));
// after
var all = folder.Search(SearchOptions.None, query);
var page = all.Skip(0).Take(10).ToArray();

if (folder is not ImapFolder)
    pageResultsLocally(folder, query);
else
    results = folder.Search(SearchOptions.None, query, partialRange);

bool supportsPartialSearch = folder is ImapFolder;

try {
    results = folder.Search(SearchOptions.None, query, partialRange);
} catch (NotSupportedException) {
    var all = folder.Search(SearchOptions.None, query);
    results = all.Skip(skip).Take(take).ToArray();
}

When it happens

Trigger: Calling MailFolder.Search(SearchOptions, SearchQuery, PartialRange, CancellationToken) (or its overloads) on a MailFolder instance that has not overridden the virtual partial-search method — e.g. after the argument checks pass (query non-null, no SearchOptions.All flag) the virtual body throws.

Common situations: Using a non-IMAP folder (such as a local maildir/memory folder or a POP3-derived folder), or calling partial-range search before the folder is an ImapFolder that advertised the required capability.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• The folder does not support partial sorts.
• The IMAP server does not support the PARTIAL extension.
• The IMAP server does not support negative partial ranges.
• The SearchOptions.All flag cannot be combined with a…
• The IMAP server does not support the METADATA extension.

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/5b91ff1bcd585062. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/MailFolder.cs:8644

		/// </exception>
		/// <exception cref="System.IO.IOException">
		/// An I/O error occurred.
		/// </exception>
		/// <exception cref="ProtocolException">
		/// The server's response contained unexpected tokens.
		/// </exception>
		/// <exception cref="CommandException">
		/// The command failed.
		/// </exception>
		public virtual SearchResults Search (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));

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

			throw new NotSupportedException ("The folder does not support partial searches.");
		}

		/// <summary>
		/// Asynchronously search the folder for messages matching the specified query, returning only the specified range of results.
		/// </summary>
		/// <remarks>
		/// <para>Asynchronously searches the folder for messages matching the specified query, returning only the
		/// search results within the specified range.</para>
		/// <para>Positive positions within the <paramref name="partialRange"/> range are relative to the oldest matching
		/// message while negative positions are relative to the newest matching message. For example, a range of
		/// <c>1:500</c> will return the oldest 500 results while a range of <c>-1:-500</c> will return the newest
		/// 500 results.</para>
		/// <note type="note">If the range specified by <paramref name="partialRange"/> references results beyond the end
		/// of the complete set of matching messages, then the results will only contain the unique identifiers that
		/// fall within the range (if any).</note>
		/// </remarks>
		/// <returns>The search results.</returns>
		/// <param name="options">The search options.</param>

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