GMass Alternative for Cold Email Software With Outlook Support and Unlimited Mailboxes

GMass built its following by being the simplest way to send mail merge and bulk email straight from Gmail. It installs as a Chrome extension, lives inside the inbox you already use, and you can have a campaign out the door in minutes. At low volume, for a solo sender who works in Gmail, that simplicity is a real strength and the price is hard to beat.

The limits show up the moment you push past a single Gmail inbox sending modest volume. GMass is tied to Gmail, so there is no native Outlook or Microsoft 365 support, and every account inherits Gmail's daily sending cap. It dropped native warmup in 2023, it does not find prospects for you, and its reporting stops at opens, clicks, and bounces with no inbox-placement view. A strong alternative keeps the fast start but adds the parts a real cold email operation needs: any inbox provider, many rotated mailboxes, warmup, leads, and deliverability you can actually see. That is the lane ColdMailer is built for.

No. GMass works only with Gmail and Google Workspace. It runs as a Chrome extension inside the Gmail interface, so there is no native Outlook or Microsoft 365 sending. If your team is on Outlook, GMass is not an option without moving your outbound into Gmail first, which is exactly why so many searches for a GMass alternative add the word Outlook.

ColdMailer takes any inbox. Connect Outlook, Microsoft 365, Gmail, Amazon SES, SendGrid, or a custom SMTP server and send from the accounts and domains you already own. You are not forced onto one provider, and you can mix inboxes across providers in the same campaign for rotation. If sending from your own server matters to you, our SMTP email sender page covers how bring-your-own-SMTP sending works in detail.

GMass sends through Gmail, so it inherits Gmail's daily limits: roughly 500 emails a day on a personal Gmail account and 2,000 a day on a paid Google Workspace account, all from a single inbox. For cold outreach the safe number is far lower than the technical cap, because a new or lightly warmed inbox should send only 20 to 50 cold emails a day to protect its reputation. GMass does offer a ColdSMTP server to exceed Gmail's limits, billed at about $0.50 per 1,000 emails, with the first 10,000 included.

The deeper issue is concentration. Pushing all your volume through one Gmail inbox stacks all the reputation risk on a single account, so one bad week can sink your sending. ColdMailer spreads the same volume across unlimited owned mailboxes with automatic rotation, so no single inbox carries the load. To see how many inboxes a target daily volume actually needs, use the email warmup calculator at the top of this page.

Not anymore. GMass retired its built-in email warmup feature in 2023, so the tool no longer warms your inbox for you. If you send cold email from a fresh domain or a cold inbox, you now have to add a separate warmup service alongside GMass, manage it yourself, and hope the two play well together. For a product aimed at cold senders, that is a meaningful gap, because warmup is one of the few things that reliably keeps cold mail out of spam.

ColdMailer keeps warmup native. New domains ramp on a safe schedule, sending volume stays inside healthy daily limits per inbox, and a mailbox pauses automatically when its reputation signals weaken. Warmup, sending, and monitoring all run in the same place, so there is no second tool to wire up. Before a campaign goes out, run the copy through the cold email spam checker to catch trigger words that warmup alone will not fix.

After its January 2026 increase, GMass has three individual plans: Standard at about $29.95 a month, Premium at about $39.95 a month, and Professional at about $59.95 a month, with annual billing lowering the monthly figure. Premium is the tier that adds inbox rotation through MultiSend and A/B testing. On top of the plan, sending over Gmail's limits through the ColdSMTP server costs about $0.50 per 1,000 emails after the first 10,000.

That sticker is only part of the real cost, the same way it is with most cold email tools. To run cold outreach properly with GMass you would still pay for a separate warmup tool, a lead source, and a verifier, and you remain capped by Gmail per inbox. ColdMailer folds leads, AI writing, warmup, and unlimited owned mailboxes into one plan you can start free, so the working cost stays predictable. For a full breakdown of where cold email spend really goes, see how much cold email software costs.

GMass is, at heart, a sending layer on top of Gmail. To run a complete cold campaign with it you usually add a prospecting tool to find leads, a verifier to clean them, and a warmup service to protect deliverability, then move data between those tools and Gmail by hand. Each piece is another subscription and another export-import step, and you are still boxed into Gmail at the end of it.

ColdMailer collapses that stack into one platform. Scrape prospects from LinkedIn, verify and enrich their emails, let AI draft a unique message per prospect, warm your domains, and send from your own rotated mailboxes across any provider, all without leaving the tool. The result reads less like a Gmail plugin and more like the outbound system a team actually runs. If you want genuinely per-prospect copy rather than merge tags, the AI email personalization engine writes each email from the prospect's role and company context.