ColdSire:
The Ultimate Review (2026)

ColdSire positions itself as a premium cold email infrastructure provider that scales. Trusted by over 5,000 companies and 500 agencies, they have managed over 40,000 domains and set up more than 100,000 mailboxes. Their core value proposition is providing Google Workspace and Microsoft 365 mailboxes from a "premium mixed pool." According to their site, they cap the share of cold email accounts in their pool at 15%, meaning your accounts sit alongside real businesses rather than in flagged cold email farms. They also emphasize true domain isolation, ensuring each domain gets its own dedicated workspace.

Trustpilot: 2.6/5 (6 reviews)

Mentions of ColdSire on Reddit are relatively sparse but generally positive regarding functionality. In the thread Cold email works! here's my experience/recommended tools, one user noted: "I used Coldsire to help save time spinning up inboxes."

In the thread Any advantage to buying Google inboxes vs sending with inboxes from domain host?, another user mentioned ColdSire as a verified reseller option: "GWS resellers have the majority hold in the market right now. I'd recommend a verified reseller who can sync to your sequencer for you." However, their low Trustpilot score suggests that the broader user experience may be inconsistent.

🟢 Premium Mixed Pool: By mixing cold email accounts with real business traffic (capped at 15%), ColdSire aims to provide a more natural sending profile, potentially improving deliverability.
🟢 Domain Isolation: Providing a dedicated workspace for each domain prevents cross-contamination, ensuring that one bad campaign doesn't ruin the reputation of your other domains.
🟢 Simple Pricing: At a flat $6 per account for either Google Workspace or Microsoft 365, the pricing is straightforward and easy to understand.

🔴 Low Trustpilot Rating: A 2.6/5 rating on Trustpilot is a significant red flag, indicating that a substantial portion of their user base has had negative experiences, possibly related to support or reliability.
🔴 No SMTP Option: ColdSire only offers Google Workspace and Microsoft 365. If you need high-volume, cost-effective SMTP mailboxes, you will need to look elsewhere.
🔴 Higher Per-Mailbox Cost: At $6 per mailbox, scaling to hundreds of accounts becomes significantly more expensive compared to dedicated infrastructure providers.

Maildoso is a cold outreach infrastructure provider – we offer domains, SMTP mailboxes, and Google Workspace accounts. The company was founded in August 2023 in Granite Bay, California, by Nikita Bykadarov (Nikita Maildoso).

While other providers offer shared or dedicated IPs, we have developed IP rotation. This means your emails are sent from hundreds of different IPs (making it harder for spam filters to detect a sending pattern), and whenever any IP gets blacklisted, we automatically swap it out for a clean one.

We have also implemented self-healing mailbox technology, which both restores burned-out mailboxes and protects your active email accounts.

The result? As of May 2026, the spam rate across our entire network of mailboxes is around 5%.

G2: 4.7/5 (181 reviews)

"Tried it mainly because of the good price, but ended up sticking with it since deliverability’s been pretty stable so far" – Thinking about trying "Maildoso". Has anyone here used it? Is it actually better than other tools?

"I tested a small batch first and results were comparable to our Google setup. Ended up moving more campaigns there because of the lower cost. That's a good strategy, buy small package and compare with your current setup" – I want to try Maildoso. What do you guys think about it?

🟢 Dynamic IP Rotation: We rotate your IP addresses in real-time – if an IP gets flagged or blacklisted, we instantly swap it for a clean one before your campaign takes a hit.
🟢 Self-Healing Rotation: An automated resting period for mailboxes every two weeks that clears provider flags and recovers reputation on autopilot.
🟢 API & MCP Automation: Create domains and mailboxes, export to your sequencer in one call – or manage it all from your AI assistant through our MCP server.

🔴 Conservative Limits: We suggest sticking to 15 emails a day per box to keep your domains healthy for the long run.
🔴 Google/SMTP Focus: We do not support Microsoft 365/Outlook/Azure environments at this time.
🔴 Lack of built-in warmup. We do not have an integrated warm-up yet, but we are currently working on it.

It’s tempting to choose a provider based solely on the lowest price, but budget infrastructure often leads to hidden costs. When deliverability drops, the consequences usually show up in three areas:

• Burned Leads: High-quality B2B data is expensive. If emails land in spam, those contacts never see the pitch, and the budget spent on data is lost.
• Damaged Domains: Fixing a domain flagged by spam filters can be a massive headache. Often, it’s easier to just buy a new one and start the warm-up process all over again.
• Missed Revenue: Every missed inbox is a missed meeting. In B2B sales, losing even one connection can mean missing out on thousands in closed revenue.

Cold email infrastructure is better viewed as an investment. Maildoso provides the technical tools to protect domain reputation and help keep emails in the primary inbox.

We have carefully reviewed ColdSire, and we have come to the conclusion that it is better to avoid this tool.

It is not entirely clear which IPs ColdSire uses, and their website does not explicitly state that they use official accounts with business licenses.

Consequently, there is a risk that you might end up with EDU profiles originating from third-country IPs, all while paying twice the market rate.

We recommend using reliable resellers instead—such as Zapmail, Inboxkit, or us.