Top 7 Email Continuity Solutions for Microsoft 365 (2026)

“Not stated” means we didn’t find it in the public documentation we reviewed. It does not mean the capability is missing, so it’s a good question for the vendor.

• Mail path: Mimecast must sit in your mail flow, inbound and outbound, at all times, not just during an outage. This is how it keeps the rolling copy.
• Failover: An administrator triggers a continuity event from the Mimecast console for all users or only an affected group. Confirm during evaluation which steps are automatic and which need an administrator.
• Access: Outlook for Windows, a native Mac app, or a mobile app, with calendar information available.
• Duration: Up to seven days per outage.
• Failback: When the mail server returns, Mimecast reconnects and synchronizes mail sent and received during the outage automatically.
• Internal mail: journaling captures internal messages as well as external ones.

Mimecast has automatic failback, and administrators manage events from a single console. The 100% service availability SLA is a vendor claim to read closely in the contract, and it does not mean zero downtime for your users.  Mailbox Continuity operates separately from your primary mail server during an outage, but it is not an independent, standalone solution: it is part of the Mimecast platform and requires Mimecast to sit in your normal mail flow. This solution makes the most sense if you already route mail through Mimecast.

Watch-out: someone has to decide to trigger failover, and continuity is capped at seven days per outage.

• Type: full-suite hot standby.
• Standby targets: Google Workspace or on-premises Microsoft Exchange. Documents can also be replicated (to Google Drive or SharePoint).
• What’s synchronized: Complete mailbox with all email messages, contacts, calendar, and tasks, plus all the inherent details like recurrences, categories, and flags. Optionally, you define a start date for the synchronization to not bring historical data that you don’t need.
• Failback: Data created in the standby can be merged back. You can select which mailbox data to merge back, with any combination of email, calendar, contacts, and tasks. Failback starts automatically as soon as the primary environment is available.
• Synchronization frequency: defined by “Polling interval” setting, in seconds.
• Environments: Support for Microsoft 365 Government, GCC High, DoD, Secret, and air-gapped networks via data diodes.

This solution gives team members access to a synchronized standby mailbox with mail, contacts, calendar, and tasks, rather than just sending and receiving mail. Users usually appreciate being able to use the calendar, scheduling and responding to appointments normally.  This solution lets the two environments coexist for as long as needed, with no time limit. For architecture details or compliance documentation for your environment, contact us directly.

Watch-out: the standby is a second environment to license, secure, and include in your compliance scope. Whether it’s Google Workspace or on-premises Exchange, evaluate how familiar your team is with the interface before committing.

• Type: full-suite hot standby
• Standby target: Google Workspace
• What’s synchronized: mail (initial sync covers the last 30 days) and calendar (18 months back and forward). CloudM’s website also lists contacts and files as add-ons, but the support documentation we reviewed describes only mail and calendar.
• Failover: users log into Google Workspace. Data freshness depends on the sync tier: weekly, daily, or hourly.
• Failback: an administrator starts a Recovery Sync after Microsoft 365 returns, reviews the per-user results and retries failures. Recovery covers mail only. Calendar changes made in Google aren’t returned and may be overwritten.
• Synchronization frequency: weekly, daily, or hourly.
• Licensing and packaging: from $1.00 per user per month for weekly sync; daily and hourly sync require a personalized quote.

Watch-out: the $1.00 entry price covers weekly sync only, so the standby can be up to a week behind; daily and hourly tiers are quoted. CloudM’s website describes automatic reverse sync, while its support documentation describes an administrator-started, mail-only recovery. Ask which applies to your deployment, and what happens to calendar changes made during an outage.

• Outbound: Mail routes through Proofpoint’s outbound relays using your normal domain identities, so recipients see no operational disruption.
• Failback: When the primary server recovers, and upon administrator intervention, queued and sent messages unspool back to Microsoft 365 with original SMTP headers intact for compliance and forensic tracking.
• Packaging: You need one of the Proofpoint Essentials tiers (Beginner, Business, Advanced, Pro).

Proofpoint’s public information on this product is very scarce. There are mentions of an Enterprise Continuity solution, but we couldn’t confirm whether it is still available, as the most recent document we found was a 2021 datasheet for Australia.

Watch-out: access is limited to a web portal, and users can’t see mail delivered before the outage unless the organization also licenses Proofpoint’s Email Archiving module. Make sure you know which tier and modules you’re being quoted and what history users will see.

• Integration: An MX record change or an IMAP connection.
• Data handling: No export and no sync to local clients.
• Failback: Unlike others, mail sent and received during the outage stays in the webmail mailbox. Users forward messages to their regular mailbox or export them as .eml files, and Retarus recommends keeping webmail access on for a grace period.
• Packaging: Continuity is listed as a feature of Retarus Email Security; confirm with Retarus whether it can be purchased on its own.
• Setup: Requires a workshop with a Retarus consultant, advance provisioning of each user’s emergency mailbox, and each user setting a password beforehand. If a user forgets it during an outage, an administrator must issue a reset token.

Retarus keeps running whether Microsoft 365 or on-premises Exchange fails, and the service runs separately from your regular infrastructure, so tests and failovers don’t disturb production. The restricted, webmail-only design can be seen as a plus for data control or an annoyance for users, given the setup and failback procedures.

Watch-out: Users don’t get Outlook, and the history window is short.

• Requirement: OpenText Email Threat Protection (or Advanced Email Threat Protection), which sits in your mail path.
• Access: a web portal, or the continuity mailbox added to Outlook as a POP or IMAP account.
• Data location: a choice of U.S., U.K. or Swiss data centers.
• Lineage: AppRiver became part of Zix in 2019, and Zix became part of OpenText in 2021.

Failover is automatic: inbound mail is spooled while your mail system is down, users can read, reply and compose against 30 days of inbound messages, and spooled mail is delivered when service returns. The product is built for MSPs serving small and medium businesses, which makes it a good fit for smaller or managed environments.

Watch-out: it requires OpenText’s email threat protection, so it’s a weaker fit for larger enterprises with their own gateway.

• Requirement and setup: Email Gateway Defense must sit in your mail path. Before an outage, administrators enable spooling for each domain and set Email Continuity to Auto-Enable.
• Failover: automatic. Barracuda starts spooling as soon as it detects your mail server is offline, and continuity begins about 10 minutes later.
• Access: users work in the Email Gateway Defense web interface, where they can read, compose, reply, forward and download messages as .eml files. There’s no Outlook access.
• Failback: original headers and timestamps of mail sent and received during the outage are synchronized to your primary mail server. Continuity stays active for up to an hour after mail starts flowing again.
• Outbound control: messages sent during an outage are still subject to your outbound policies.

Barracuda’s continuity is built into Email Gateway Defense and needs no one to trigger it, which makes it one of the more hands-off options here once configured.

Watch-out: continuity switches off after 96 hours, so ask what happens to mail after that point. Also, if you use LDAP authentication and your LDAP server goes down, users can’t log in to Email Continuity, which matters in cyberattack scenarios where the directory may be affected.

• Intermedia. Best known as a hosted Exchange provider, Intermedia publishes a support guide titled Email Continuity for Microsoft 365 (User Guide), which suggests a current offering. We could not find a public datasheet covering retention, failover behavior, or certifications, so we did not include it. Historically, its continuity add-on was McAfee Email Continuity, a product line that has since been retired (see below).
• Fortinet FortiMail. A 2021 Fortinet blog post describes a 30-day rolling mail store and webmail access when the gateway runs in server mode. The current FortiMail email security page doesn't mention continuity, so we left it out. If it matters to you, ask Fortinet for current documentation.
• Hornetsecurity. A product listing describes a continuity service that activates when a mail server failure is detected, with POP3/IMAP or webmail access and a stated 99.9% availability. We found no current public datasheet, so it is an honorable mention rather than an entry.
• Trend Micro Email Security. Trend Micro’s current documentation describes a Continuity Mailbox that lets users access email when the primary mail server is unavailable. However, we could not find enough public product-level detail on retention, failover activation, duration limits, failback behavior, or packaging to compare it consistently with the seven entries above. Ask Trend Micro which Email Security plans include the feature and how it is configured for Microsoft 365.

Several older brands still draw searches for "email continuity." Here is what became of them.

• McAfee (including MX Logic). McAfee acquired MX Logic in 2009. In 2015, when McAfee was part of Intel (operating as Intel Security), the company announced end of life for its SaaS email line, including email protection and continuity. Sales stopped January 11, 2016, and the services were scheduled to stop working altogether on January 11, 2021.
• Symantec. After Broadcom's 2019 acquisition, Symantec streamlined its portfolio. For example, Mail Security for Microsoft Exchange entered end of life in 2022. Administrators have been discussing the discontinuation of Symantec-branded email continuity offerings, as in this Spiceworks thread.
• AppRiver. Folded into Zix (2019), then OpenText (2021). Its continuity product lives on as OpenText Core Email Continuity, mentioned in our analysis.
• Veritas. Veritas Technologies separated its Data Compliance, InfoScale, and Backup Exec businesses into a new independent company, Arctera, in December 2024. Email continuity now appears in Arctera’s documentation as an add-on to Arctera Personal Archive that turns the archive into a secondary gateway during an outage. It’s an archive add-on, not a standalone continuity solution.

1. Failover: is it automatic or administrator-triggered, and how long does it take?
2. History: how much past mail can users see during an outage, and can they see mail delivered before it began?
3. Duration: is there a cap on how long continuity can run?
4. Scope: mail only, or calendar, contacts, and files too?
5. Dependencies: do you need the vendor's gateway or security product to use it?
6. Security during failover: is mail still scanned, and do your outbound and DLP policies still apply?
7. Data location and sovereignty: Is the vendor in your mail path all the time or only during an outage, and in which jurisdiction is that mail stored and processed, including for support access?
8. When Microsoft is degraded: how does your service behave when Microsoft delays delivery rather than going fully down? Vendors' own incident reports show these edge cases happen: on January 22, 2026, Hornetsecurity reported deferred mail alongside an ongoing Microsoft incident.
9. Cost: per user or per domain, and what else must you buy?
10. Testing: can you run a failover test without affecting production?

Do I need an email continuity solution given current uptimes?

A 99.9% uptime commitment sounds strong until you do the arithmetic: 0.1% of a 30-day month is about 43 minutes of permitted downtime, every month. Real incidents run longer than that, and they tend to arrive at the worst moment.

What should I consider for ROI of an email continuity solution?

For a budget conversation, a simple formula helps to frame productivity cost: employees affected × share of their productivity affected × hourly cost × outage hours. As an illustration, take 500 employees who spend about 25% of their time on email, at roughly $36 an hour (a $75,000 salary spread over 2,080 hours), during a three-hour outage: 500 × 0.25 × $36 × 3 ≈ $13,500 in lost productivity, before counting missed customer messages or the helpdesk load. Use your own numbers; the point is that one avoided outage can pay for a good part of a year of continuity.

Did vendors pay to be included?

No. See the disclosure at the top about Connecting Software's own entry.

What's the difference between email continuity and email backup?

Continuity keeps people sending and receiving during an outage. Backup restores data after loss. Most organizations eventually want both.

Can continuity solutions also cover documents?

Yes, business continuity solutions also exist for documents. For example, Connecting Software offers its Secure Sync range, which covers document synchronization environments such as Microsoft 365, SharePoint, OneDrive, Google Drive, and Nextcloud.

How often is this updated?

Products in this category change frequently. Check the "Last updated" date at the top and confirm details directly with vendors before you buy.