jstedfast/MailKit · error · NotSupportedException

The SAVEDATESUPPORTED search term is not supported by the…

Error message

The SAVEDATESUPPORTED search term is not supported by the IMAP server.

What it means

BuildQuery throws this NotSupportedException when a SearchQuery.SaveDateSupported term is used but the server lacks the SAVEDATE capability (RFC 8514). SAVEDATESUPPORTED matches messages whose savedate is supported; saving date is a server-stored timestamp of the last modification. MailKit checks ImapCapabilities.SaveDate during query serialization and fails fast.

Solutions

Check (client.Capabilities & ImapCapabilities.SaveDate) != 0 before using any SaveDate-related search term.
Substitute internal-date-based queries (DeliveredBefore/DeliveredSince) which approximate the last-modification time.
Upgrade the IMAP server to a version implementing SAVEDATE if savedate semantics are required.

Example fix

// before
var uids = folder.Search(SearchQuery.SaveDateSupported());

// after
if ((client.Capabilities & ImapCapabilities.SaveDate) != 0)
    uids = folder.Search(SearchQuery.SaveDateSupported());
else
    uids = Array.Empty<UniqueId>(); // savedate not available on this server

Defensive patterns

Strategy: validation

Validate before calling

if ((client.Capabilities & ImapCapabilities.SaveDate) == 0)
    return Array.Empty<UniqueId>(); // savedate terms unusable

Type guard

bool SupportsSaveDate(ImapClient c) => (c.Capabilities & ImapCapabilities.SaveDate) != 0;

Try / catch

try {
    return folder.Search(SearchQuery.SaveDateSupported());
} catch (NotSupportedException) {
    return Array.Empty<UniqueId>();
}

Prevention

Treat the whole SaveDate family (Supported/Before/On/Since) as one gated feature.
Check capabilities once at connect and cache the result.
Design sync logic that does not depend on SAVEDATE for portability.

When it happens

Trigger: Calling folder.Search(SearchQuery.SaveDateSupported()) or composing it with other terms on a server without ImapCapabilities.SaveDate.

Common situations: Code relying on RFC 8514 SAVEDATE against servers that haven't implemented it (only some recent servers do, e.g. newer Dovecot); Gmail/Exchange lack it.

Related errors

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/96c0799107e36791. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Net/Imap/ImapFolderSearch.cs:291

					throw new NotSupportedException ("The OLDER search term is not supported by the IMAP server.");

				numeric = (NumericSearchQuery) query;
				builder.Append ("OLDER ");
				builder.Append (numeric.Value.ToString (CultureInfo.InvariantCulture));
				break;
			case SearchTerm.Or:
				builder.Append ("OR ");
				binary = (BinarySearchQuery) query;
				BuildQuery (builder, binary.Left, args, true, ref charset);
				builder.Append (' ');
				BuildQuery (builder, binary.Right, args, true, ref charset);
				break;
			case SearchTerm.Recent:
				builder.Append ("RECENT");
				break;
			case SearchTerm.SaveDateSupported:
				if ((Engine.Capabilities & ImapCapabilities.SaveDate) == 0)
					throw new NotSupportedException ("The SAVEDATESUPPORTED search term is not supported by the IMAP server.");

				builder.Append ("SAVEDATESUPPORTED");
				break;
			case SearchTerm.SavedBefore:
				if ((Engine.Capabilities & ImapCapabilities.SaveDate) == 0)
					throw new NotSupportedException ("The SAVEDBEFORE search term is not supported by the IMAP server.");

				date = (DateSearchQuery) query;
				builder.Append ("SAVEDBEFORE ");
				builder.Append (FormatDateTime (date.Date));
				break;
			case SearchTerm.SavedOn:
				if ((Engine.Capabilities & ImapCapabilities.SaveDate) == 0)
					throw new NotSupportedException ("The SAVEDON search term is not supported by the IMAP server.");

				date = (DateSearchQuery) query;
				builder.Append ("SAVEDON ");
				builder.Append (FormatDateTime (date.Date));

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