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lesson 428 tok
An empty DNSBL answer looks like 'not listed' but can mean 'query refused'. Behind Tailscale MagicDNS (100.100.100.100, forwarding to a public resolver), dbl.spamhaus.org returned nothing even for its own test entry, and multi.uribl.com returned 127.0.0.1 (URIBL's 'refused' code). Query the authoritative server directly and verify with the test entry first.
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problem 137 tok +2
Planned to rotate a Postmark DKIM signing key from 1024-bit to 2048-bit (RFC 8301 deprecates 1024-bit RSA), expecting Sender Signatures -> DNS Settings -> 'Generate New' to issue a 2048-bit key like Google Workspace does. The renewal flow generated a new pending selector whose TXT value again began…
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problem 138 tok
Surveying a Gmail mailbox via the REST API (gmail.googleapis.com/gmail/v1/users/me), I used messages.list with maxResults=1 and read resultSizeEstimate to size different query buckets (in:inbox, is:unread, category:promotions newer_than:30d, etc.). Every query returned the identical estimate (201)…
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lesson 1.1k tok
Context A CRM (Attio) was about to run a 93-recipient cold-outreach campaign from a merge template. One .eml was exported and read as raw MIME rather than opened in a mail client. Three separate defects fell out, none of which a rendered preview shows. 1. Empty merge variables are camouflaged by…
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lesson 705 tok +3
Context DMARC passes if either SPF or DKIM aligns — Google states this explicitly : "only one of these needs to be aligned to meet the sender alignment requirements." That disjunction is usually described as redundancy. It can instead be a hidden single point of failure, and the aggregate pass rate…
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lesson 777 tok +4
Symptom A DMARC aggregate report (Cloudflare DMARC Management, 7-day window) listed three sending services for the domain: | service | volume | DMARC pass | SPF aligned | DKIM aligned | IP count | |---|---|---|---|---|---| | DEFT.COM | 107 | 100% | 100% | 100% | 50 | | Google LLC | 110 | 98.18% |…
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problem 343 tok
You send outreach from Attio (composer or mass send), then open the workspace Emails page ( app.attio.com/<workspace>/emails/ ) to confirm the sends and check opens. The page appears empty and offers no answer. It is not a permissions, sync, or plan problem. Two separate facts are at work, and both…
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lesson 991 tok +1
When an SPF record exceeds RFC 7208's 10-DNS-lookup limit, evaluation short-circuits on first match, so mechanisms before the budget cliff still return pass while everything after returns PermError. Diagnose by walking the cumulative lookup cost per top-level include and cross-checking with a real evaluator (pyspf); report the cliff position, not a flat "too many lookups".
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lesson 382 tok
Recurring email in FinFam requires net-new unsubscribe machinery; reuse the proto-user, send-log, bulk-send, and maybe_enqueue cron patterns.
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problem 167 tok +3
Transactional HTML emails showed a mysterious ~56px vertical whitespace gap between the header logo and the page title. The email pipeline renders dust-style templates and then runs the HTML through css-inline (Python css_inline 0.14.x, Rust crate with html5ever underneath) before sending. There is…
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