Conciseness

The body is dense and operational with no explanations of concepts Claude already knows — no SMTP primer, no email-format tutorial — and specifics like "SMTP_PORT 默认 587（STARTTLS），465 使用 SSL" earn their tokens. Minor tightening is possible (the "中文" requirement and "返回格式： Subject: ... ---" boilerplate repeat across all six drafting templates and could be factored out), which matches 'efficient; minor instances that could be trimmed' rather than the fully lean level-5 anchor.

Actionability

Sending is fully executable: copy-paste bash blocks with exact flags ("--attachment \"/绝对路径/方案.pdf\""), explicit env-var contract, and JSON receipt semantics ("ok: true 表示 SMTP 服务器已接受发送"). The main gap is that the wrapper is invoked as "email-ops" via PATH while the bundle's actual file scripts/send_email.py is never referenced by path, leaving the user stranded if the command isn't installed — hence 4 rather than 5.

Workflow Clarity

A clear 6-step sequence with an early-exit rule ("用户已给出收件人、文件和发送要求时……直接执行 Step 5"), explicit validation ("任一附件不可读时不发送邮件", ok:true/false receipt handling), a safety gate ("默认行为是起草，不发送"), and an error-recovery table ("SMTP 认证失败 → 停止……告知用户"). It falls short of the level-5 anchor only because pre-send verification of the draft against the user's request is stated briefly rather than as an explicit checkpoint with a re-check loop.

Progressive Disclosure

Section structure is good (numbered steps, two well-formed tables), but the ~150 lines of six drafting templates are inlined in a 337-line SKILL.md where a references/ file would fit, and the one bundle file (scripts/send_email.py) is not clearly signaled — the body points to an `email-ops` PATH command instead of the bundled script's path. This matches 'some structure; references present but not clearly signaled; content that should be separate is inline'.

Specificity

The description names the domain and two concrete actions ("邮件起草与发送") plus concrete format support ("纯文本正文和 ZIP、PDF、图片等多个附件"), but coverage is narrow relative to the skill's actual scope (thread reading, follow-ups, proposals, meeting confirmations are unmentioned). It fits the 'names domain and 1-2 concrete actions, but not comprehensive' anchor better than the level-4 anchor, which expects several specific actions.

Completeness

Both parts are explicitly present: a clear what ("邮件起草与发送，支持纯文本正文和……多个附件") and an explicit when ("用户要求把文件发到指定邮箱时也使用本技能"). Not a 5 because the 'when' clause covers only the file-sending scenario and leaves the drafting trigger implied; not a 3 because explicit trigger guidance exists.

Trigger Term Quality

Natural user phrases are present: "邮件", "发送", "附件", concrete formats "ZIP、PDF、图片", and the scenario "把文件发到指定邮箱". A few common natural terms are missing (e.g., 回复/跟进/转发/写邮件), matching the 'good keyword coverage; a few natural terms missing' anchor rather than the comprehensive level-5 example.

Distinctiveness Conflict Risk

Email drafting/sending with SMTP attachments (ZIP/PDF/图片) is a clear niche with the distinct trigger "把文件发到指定邮箱", giving minimal conflict with unrelated skills. Minor overlap risk remains with generic file-transfer or mail-client skills since the description doesn't state what distinguishes it (e.g., SMTP-based sending), fitting the 'mostly distinct' anchor.