Service Limits

SMTP Zen succeeds when every customer’s messages quietly land in the inbox. That only happens if we keep traffic predictable and consent-based. Treat the limits below as non-negotiable: they protect your reputation as much as ours.

At a glance

• Hard ceiling: about 400 outbound emails per mailbox per hour. That includes aliases using the same login. If you have a sustained, opt-in workflow that genuinely needs more throughput, open a support ticket with concrete volume data, consent records, and why the extra capacity is required; we will review and approve only when it will not compromise deliverability for you or anyone else. Please note that there are no guarantees that the increase will be performed.
• Forbidden traffic: unsolicited marketing campaigns, cold email sequences, purchased/rented lists, affiliate blasts, or anything else a recipient did not request.

Need more than that? You probably want a bulk sender or CRM platform instead of SMTP Zen.

Traffic we welcome

• Transactional and relationship messages that people expect (receipts, onboarding, account notices).
• One-to-one or small team correspondence, including replies to support tickets.
• Modest newsletters to subscribers who opted in and can unsubscribe with one click.

Behavior we refuse

Trying to sidestep policy (multiple accounts, creative alias juggling, semantic rebranding of spam) will not work. We correlate volume across domains, watch complaint ratios, and act quickly when limits are ignored. If your strategy depends on “beating the system,” this is the wrong system.

Why the hourly cap exists

Inbox providers score every sender. Large bursts, recycled contact lists, and unverified domains drive those scores down, which means throttles, junk-folder placement, or outright blocks. By enforcing a conservative hourly rate, we keep SMTP Zen’s shared reputation clean so routine business mail keeps flowing.

Deliverability realities

• Volume without engagement looks suspicious. Even inside the cap, low open rates or repeated bounces trigger protective throttles.
• Consent trumps everything. A well-targeted list of 100 readers beats 10,000 scraped contacts every time.
• Obeying limits is the floor, not the ceiling. Healthy DNS (SPF, DKIM, DMARC), clean content, and steady pacing are still required.

Consequences & alternatives

Accounts that ignore these guardrails face rate limits, suspensions, or termination without refund. Abuse reports may be shared with upstream providers. If you genuinely need to broadcast to cold audiences or push tens of thousands of emails per hour, choose a marketing automation vendor built for that workload before you damage both our reputations.

Play within these boundaries and SMTP Zen will remain the calmest part of your communications stack.