Upgrade to 0.19.0
Keep MCP arguments within published input limits and normalize date filters before calling tools.
Fluxmail 0.19.0 publishes input limits in MCP tool schemas and rejects arguments outside those limits. Some arguments accepted by 0.18.0 now return a tool result with isError: true before the mail operation runs.
Find your migration
| Interface | Required changes |
|---|---|
| MCP over HTTP or stdio | Keep strings and recipient lists within the limits below. Trim date filters and omit blank dates. Deduplicate message IDs and split changes into batches of at most 100. |
| CLI | No client migration. |
| REST | No client migration. |
Check argument limits
Refresh the tool schemas with tools/list after upgrading. Update custom clients and saved tool calls that can exceed these limits.
| Input | Limit |
|---|---|
| IDs, including account, message, thread, draft, attachment, delivery operation and reply IDs | 512 characters |
Label names and move_emails.folder | 512 characters |
Search strings on list_emails, search_emails, and search_emails_batch, including query, text, search folders, sender, recipient, subject and provider query filters where available | 2,048 characters |
get_thread.pageToken | 1,024 characters |
Each to, cc, or bcc list on create_draft, update_draft, preview_send, and send_email; each to or cc list on forward_email | 100 recipients, each at most 512 characters |
Subject on create_draft, update_draft, preview_send, and send_email | 998 characters |
Attachment filename, mimeType, and contentId | 255 characters each |
messageIds on tools that change messages | 100 entries, counting duplicates |
Use IDs and page tokens returned by Fluxmail without modifying or truncating them. Shorten search text, subjects or attachment filenames in your application when needed. Keep each recipient list within its limit before drafting or sending.
Normalize date filters
On list_emails, search_emails, and search_emails_batch, pass after and before as plain YYYY-MM-DD strings. Trim surrounding whitespace before making the call. If a filter is blank, omit it or pass null.
For example, change "after": " 2026-10-01 " to "after": "2026-10-01" and omit "before": " ". Fluxmail previously trimmed these values or dropped blank filters. Invalid calendar dates were already rejected.
Split message changes
For mark_emails_read, mark_emails_unread, star_emails, unstar_emails, archive_emails, move_emails, add_labels, remove_labels, trash_emails, restore_emails, and delete_emails, deduplicate messageIds and send at most 100 IDs per call.
Previously, a call could contain more than 100 entries if there were at most 100 distinct IDs. The limit now counts every array entry, so 100 distinct IDs plus a repeated ID fails validation.
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