PowerMTA bounces.
What to do
with the recipient address.

Five tiles answer the main question about PowerMTA bounces for the period: how many there are, what type, and what to do with the addresses. Bounces are split by code — 5.X.X, where retrying won't help, and 4.X.X, where the MTA used up its retries — and by reason. 2,152 bounces will go to the suppression list — only those where the mailbox doesn't exist, while the 323 spam bounces don't go there: the mailbox exists and must not be removed. The “Bounced” tile is green — 2.9% of 124,915 recipients. 2,670 bounces have a 5.X.X code (74.5%), 912 have a 4.X.X code (25.5%). It's the split by reason, not by code, that keeps you from removing live mailboxes by mistake.

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• Bounced — 3,582 — 2.9% of 124,915 recipients, the tile is green.
• Code 5.X.X — 2,670 (74.5%) — retrying won't help.
• Code 4.X.X — 912 (25.5%) — the MTA used up its retries.
• To suppression — 2,152 — only where the mailbox doesn't exist.
• Spam — 323 — 9.0%, the mailbox exists.

The tile color follows the common bounce-rate thresholds.

The chart shows bounces by day over the nine days of the period: the bars are bounces per day, the dashed line is the bounce rate with its own scale on the right. It helps you spot a day when the bounce rate went up and work out what was sent that day. In the example the rate is steady — 2.8–2.9% on full days; incomplete days at the edges are paler and never count as the best or worst day. The bars are all one color because the MTA counts the reason breakdown only for the whole period. The best day is Oct 19 (553 bounces, 2.8%), the worst is Oct 18 (359, 2.9%). What the bounces are made of — “no mailbox” accounts for 60.1% of all bounces — you see on the categories screen below.

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• Full days — 2.8–2.9%.
• Worst — Oct 18 — 359 bounces, 2.9%.
• Best — Oct 19 — 553, 2.8%.
• Incomplete — Oct 15 and Oct 23 are paler and never count as the best or worst day.
• “No mailbox” — 60.1% of all bounces.

The bars are one color: the MTA counts the reason breakdown only for the whole period.

The categories screen shows how the MTA itself sorted the bounces: in the example 12 of the 17 categories PowerMTA knows came up. The Hub doesn't rename them, so the numbers match the accounting files on the server and you can check them. The biggest group is “no such mailbox”, 1,577 bounces (44.0%): these are the addresses to clean from your list. Mailbox full and spam rejection — 323 each: the mailbox exists, so you must not delete the address. Clicking a row opens the category breakdown on the right. Start with the top rows: the first five categories account for most of the bounces. Then come no such domain, mailbox provider policy, connection, routing, expired, other and content.

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• No such mailbox — 1,577 (44.0%).
• Mailbox abandoned — 396 (11.1%).
• Mailbox full and spam — 323 each (9.0%).
• Server didn't answer — 215 (6.0%).
• Then — no such domain, mailbox provider policy, connection, routing, expired, other, content.

Clicking a row opens the breakdown on the right.

The category breakdown shows the words mailbox providers use when they reject mail, and who exactly replies that way. In the example the “No such mailbox” category is open, 1,577 bounces: each provider has its own wording, shown word for word — “User unknown in virtual mailbox table” 472 times, Gmail's “…does not exist” 310 times. Below are the domains that bounce this way: gmail.com, yahoo.com, the corporate veltrano-group.com, outlook.com. A switch at the top turns on the “by domain” and “text × domain” views. Microsoft, for example, has its own wording — “Requested action not taken: mailbox unavailable”, 286 times. The exact line is easy to copy into a search or into an email to your hosting provider.

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• User unknown in virtual mailbox table — 472 (29.9%).
• Gmail — “The email account that you tried to reach does not exist” — 310.
• Microsoft — “Requested action not taken: mailbox unavailable” — 286.
• Yahoo — “This user doesn't have a yahoo.com account” — 222.
• Domains — gmail.com — 310, yahoo.com — 222, veltrano-group.com — 194, outlook.com — 176.

The “by domain” and “text × domain” views — with the switch at the top.

The table shows the top eight recipient domains by number of bounces — with the bounce rate and a split into “no mailbox”, “spam” and “other”. It tells you which domain has a problem and what kind: dead addresses in your list or the provider's filter. Look at the rate, not the count: gmail.com has 680 bounces, but that's 1.7%, while the corporate veltrano-group.com has 429 bounces — already 6.1%, and its row is red. The color thresholds are captioned under the table. The column totals — 2,152 “no mailbox”, 323 spam and 1,107 other — match the categories exactly. If “spam” is growing for a domain, the issue is your messages or reputation, not your list; the full domain card is on the “Domains” tab.

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• gmail.com — 680 out of 39,916 recipients — 1.7%.
• yahoo.com — 486 — 3.9%.
• veltrano-group.com — 429 — 6.1%, in red.
• outlook.com — 388 — 2.6%.
• aol.com — 5.0%, in yellow.
• Totals — 2,152 “no mailbox”, 323 spam, 1,107 other.

Color thresholds: under 4% — green, from 4% — yellow, from 6% — red.

The vMTA table shows all 23 sending points with the same bounce split and the worst domain for each. It helps you understand the cause: the sending address or the recipient. A domain counts as the worst only if it has at least 0.5% of this vMTA's messages and at least 50 messages, so even a small point can compare its domains. In the example all 23 points have the same worst domain — veltrano-group.com, from 3.8 to 11.1% bounced: the problem isn't the sending addresses but the recipient domain. If, on the other hand, one point stands out across all domains, that's the one to dig into — on the “vMTA” tab. The table totals are the same 2,152 “no mailbox”, 323 spam and 1,107 other.

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• Bank — secure. and id.corvalis-bank.org-vmta — 38 thousand recipients each, 2.2%.
• Worst domain — for all 23 — veltrano-group.com, 3.8–11.1%.
• Threshold — a domain counts from 0.5% of the point's messages and from 50 messages.

When the same problem shows up on every sending address, it's the recipient domain.