When a test email seems lost, check Junk before debugging your pipeline
Testing a newly-deployed email-processing pipeline by sending a fresh email from a known address to a target inbox, and finding nothing arrived on the receiving side.
Before investigating sync agents, queue states, or container logs, check the recipients spam/junk folder via the providers web UI. Aggressive spam filtering on Outlook, Gmail, and most enterprise mailboxes will silently route test-pattern emails (generic subjects, low-reputation senders, new sending domains, or unfamiliar from addresses) into Junk — meaning the IMAP poller never sees them because most setups only sync the Inbox folder. A clean signal that the email did NOT land in the Inbox: the IMAP server-reported exists count for the Inbox does not increase between polls. If exists is stable but you definitely sent something, junk routing is the answer ~80% of the time before considering pipeline bugs. Multi-folder IMAP sync (including Junk) is a worth-doing feature for any pipeline that needs to surface false-positive spam-filtering, but in the meantime: check the junk folder first.
When a test message does not appear in a downstream pipeline, check the recipient inboxs IMAP exists count (or the providers UI) for any growth — if exists is unchanged, the message went to junk/spam or never delivered. Save the deep pipeline debugging for cases where exists actually advanced.