Emails a month
Transactional and automation emails together.
Contacts
People you keep in the tool. Customer.io and Loops bill by these.
Delivery provider for Senlo
Senlo does not deliver email; your provider does, at its own price.
Your time on a self-hosted install
Upgrades, backups, the odd restart. Set it to what it really is for you.
Per month at 50,000 emails and 10,000 contacts
Customer.io Essentials, billed by profiles: $100 for 5,000, then $0.009 each. Delivery included. | $145 | |
Loops Billed by subscribed contacts, sends unlimited. Delivery included. | $99 | |
Senlo Cloud + Amazon SESCheapest here Pro $19 + Amazon SES $5. | $24 | |
Self-hosted Senlo + Amazon SES ≈ $8 server + Amazon SES $5 + your time $50 (1 h × $50). | $63 |
Delivery only, for reference
What the provider alone costs: no editor, no automations, templates in your code. Not the same product, so not on the chart.
Price as you grow
Both axes on a log scale. Contacts grow with emails at your ratio (5 emails a contact). The dashed vertical line is where you are now.
On this line Customer.io costs more than Senlo at every volume: Essentials starts at $100 a month with no free plan.
Where Senlo is not the cheapest
Said here so you do not have to find it in the comments.
- Tiny volumes: up to 1,000 contacts and 4,000 sends Loops is free with delivery included and no second account. Senlo Free with Resend's free tier is also $0, but it is two accounts.
- Many emails to a small list: Loops does not charge per send, so 50,000 emails to 2,000 contacts costs $49 on Loops and $74 on Senlo Pro with Postmark.
- Above 250,000 emails a month Senlo Cloud has no plan. The Senlo option there is self-hosting (MIT), and that costs your time.
- Customer.io has a Startup Program: up to 12 months free with up to 30,000 profiles for companies that raised under $10M and were never customers before. If you qualify, it is $0 for that time.
Where the numbers come from
Each price was read from the vendor's own page on the date given. List prices, billed monthly, in USD, before tax.
- Customer.io Essentials: $100 a month with 5,000 profiles and 1,000,000 emails, then $0.009 per profile and $0.12 per 1,000 emails. Premium from $1,000 a month, billed yearly. Checked 2026-11-02, customer.io/pricing. Startup Program terms checked 2026-11-02, customer.io/solutions/startups.
- Loops: free up to 1,000 subscribed contacts and 4,000 sends; Growth from $49 for 5,000 contacts up to $4,799 for 1,500,000, sends unlimited. Checked 2026-11-02, loops.so/pricing.
- Senlo Cloud: Free up to 3,000 emails and 1,000 automation runs for one person; Pro $19 up to 50,000 emails, 10,000 runs and 5 people; Team $59 up to 250,000 emails, 100,000 runs and unlimited people (pricing). Above 250,000 emails: self-host, or write to us.
- Resend transactional plans, checked 2026-11-02 (resend.com/pricing). Postmark Basic, checked 2026-11-02 (postmarkapp.com/pricing), no public price above 300,000. Amazon SES at $0.10 per 1,000 emails, checked 2026-11-02 (aws.amazon.com/ses/pricing).
- Self-hosted Senlo: about $8 for a 4 GB VPS running Postgres, Redis, the app and the worker, an estimate rather than a quote. Your time is the line you set above.
Questions
- Why do Senlo's rows include a provider's price?
- Because Senlo does not deliver email. It renders the template and runs the automation; Resend, Postmark or SES delivers it from your domain and bills you for that. Customer.io and Loops include delivery in their price, so a fair total for Senlo has to add the provider.
- Why are Resend and Postmark not on the chart?
- On their own they only deliver: no visual editor, no automations, templates live in your code. They are cheaper than any row on the chart and do a different job, so they appear under the table for reference and not as a competitor.
- What counts as a contact?
- Customer.io bills by profiles, people and objects, and profiles deleted during the billing cycle still count. Loops bills by subscribed contacts; people who only get transactional email do not count, so if most of your list never enters an automation, Loops costs less than shown. Senlo Cloud does not bill by contacts at all.
- Is self-hosting Senlo really this cheap?
- The code is free (AGPL-3.0). The server is about $8 for a 4 GB VPS, and the provider bills as usual. The real cost is your time on upgrades and backups, which is why the calculator adds it as a line you set yourself.
- How fresh are the prices?
- Every price was read from the vendor's own pricing page on the date shown under the calculator, and they are rechecked monthly. If a number is wrong, open an issue on GitHub with the link and it gets fixed.
- Can I link to my numbers?
- Yes. The address bar follows the sliders, so the link in it, or the one the copy button gives, opens the calculator on the same case. For example /calculator?emails=50000&contacts=20000&provider=resend.
More comparisons
Senlo next to other products, with the same honesty about what it does not do. All comparisons.
Senlo vs Customer.io
For teams that use Customer.io for transactional email and onboarding flows and pay per profile for a marketing suite around it.
Senlo vs Loops
For products on Loops that want flows which call their own API, pay for sends rather than contacts, and keep delivery with their own provider.
Senlo vs Brevo
For products that use Brevo for transactional email and onboarding flows, not campaigns, and want their own provider and no contact caps on the tier.
Senlo vs Mandrill
For teams on Mailchimp Transactional who pay for a Mailchimp plan only to keep Mandrill, and want templates that are not tied to the sender.
Senlo vs React Email
For teams that write emails as React components and want people who do not write code to edit them without a pull request and a deploy.