Knowledge base
Three families of limit, applied at oncecriticalWritten by the HubmechanismA delivery is governed by the domain limits, the address limits and the connection limits simultaneously, and the strictest of everything that matches decides.Where held-back mail goes, and why their names matterimportantmechanismMail held back by a rate limit, a flood pattern, a pause or greylisting is moved into a queue created on the spot and named after what is holding it.Set limits for a warm-up stagecriticalWritten by the HubprocedureProfile, rule, reload, read back — with the two rules that make it safe: one target per rule, and never write meaningful for a switch nobody chose.to: domain (id)importantqueueCreated on the fly when a limit, a pause or greylisting holds mail back, and named after what is being held.Email ThrottlingcriticalWritten by the Hubconsole screenWhere a throttle profile is built — forty-two settings in eight groups — and bound to the traffic it governs.Flood PatternsimportantWritten by the Hubconsole screen"When a receiver answers like this, hold back for a while" — a temporary throttle triggered by a response.MX Pattern GroupingimportantWritten by the Hubconsole screenTreats every domain whose mail is handled by the same servers as one destination for throttling.IP Range Groupingconsole screenThe same grouping idea, applied to the address ranges of the receiving servers.Email Throttle Schedulesconsole screenThe engine's own warm-up: a schedule of steps, each adding a throttle profile on a given day.capacitycriticalWritten by the Hubdatabase tableOne row is a complete delivery profile: message and connection limits per domain and per address, seventeen SMTP timeouts, TLS mode and behaviour on unexpected responses.capacity_rulescriticalWritten by the Hubdatabase tableBinds a throttle profile to a domain, a sending address, a pool — or any combination, with blanks meaning "any", and each such combination belongs to exactly one profile.flood_responsesimportantdatabase tableA throttle profile that switches itself on when a receiving server says something matching a pattern, and switches itself off after a set time.mx_pattern_groupsimportantWritten by the Hubdatabase tableNamed groups that MX patterns belong to, usable wherever a domain can be named.mx_patternsimportantWritten by the Hubdatabase tablePatterns matched against a domain's MX records, so domains served by the same provider fall into one group.response_patternsimportantdatabase tableMatches what a receiving server said, narrowed by destination, sending address, pool and tag, in priority order.capacity_schedulesdatabase tableA named schedule that raises limits over days; left empty on our nodes by decision.ip_rangesdatabase tableAddress ranges of receiving servers, grouped so that limits can apply to a whole network.response_actionsdatabase tableThe things that can happen when a response matches: pause, suppress, retry, add or remove an address or tag, set a property on the message or on the result.capacity_schedules_rulesdatabase tableBinds a schedule to combinations of sending address and destination domain.capacity_schedules_statesdatabase tableThe engine's own record of which day of a schedule each address-and-domain pair has reached.capacity_schedules_stepsdatabase tableOne row per step: from this day of the schedule, add this throttle profile to the ones already in force.ip_range_groupsdatabase tableNamed groups of receiver address ranges.response_patterns_actionsdatabase tableMany-to-many link between triggers and actions, with its own ordering.domain_maxmessagescriticalWritten by the Hubdatabase fieldHow many messages a minute may be sent to one destination domain, across every sending address.ip_maxmessagescriticalWritten by the Hubdatabase fieldThe per-address half of the limits: the same six quantities, counted for the pair of sending address and destination rather than for the destination alone.localipcriticalWritten by the Hubdatabase fieldThe sending address this rule applies to; empty means all of them.domainimportantWritten by the Hubdatabase fieldThe destination this rule's profile applies to; empty means every destination.domain_maxconnectionsimportantWritten by the Hubdatabase fieldHow many SMTP connections to one domain may be open at the same time.domain_maxconnectsimportantWritten by the Hubdatabase fieldHow many new connections a minute may be opened to one domain.patternimportantdatabase fieldWhat the receiving server said, matched against its response text.finaldatabase fieldWhether remaining triggers are skipped once this one has matched.maxqueueWritten by the Hubdatabase fieldHow many messages for this destination are held in the engine's memory at once.pool_idWritten by the Hubdatabase fieldRestricts a rule to addresses in one pool.typedatabase fieldExact, substring, wildcard or regular expression.domain_maxbytesdatabase fieldBandwidth ceiling towards one domain, counted in bytes per minute.precedencedatabase fieldNot a priority at all: the engine stamps the moment the profile was created and uses it to keep the console list in a stable order.The transfer was refusedimportantdelivery stateThe receiver refused the DATA command, before any content was sent.