WatchGuard firewall: allow apostrophe in email addresses

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To allow the apostrophe in email addresses with WatchGuard firewalls, it’s necessary to modify the SMTP-proxy configuration.

Even if apostrophe character is allowed in email addresses (ex. simon.o’connor@domain.com), if an external user tries sending an email to your network protected by WatchGuard firewall, the system may returns the sender the message of unavailable mailbox.

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Procedure

Because SMTP-proxy by default doesn’t allow the character “ ”, it is necessary to edit some settings to allow the apostrophe.

Open WatchGuard System Manager then Policy Manager. Right click the SMTP-proxy rule then select Modify Policy option.

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Click the View/Edit Proxy button in the right side of Proxy action field.

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Senders’ addresses

From Address > Mail From of the SMTP-proxy, click Change View button to switch to Advanced View. Click Edit button to edit the Non-allowed characters rule.

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Add the apostrophe at the end of default Regular Expression then click OK.

from:   [^-_.+=%*/~!&@?0-9a-zA-Z]

change to:   [^-_.+=%*/~!&@?0-9a-zA-Z]     (note the ‘ at the end)

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Recipients’ addresses

From Address > Rcpt To of the SMTP-proxy, click Change View button to switch to Advanced View. Click Edit button to edit the Non-allowed characters rule.

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As done in previous step, add the apostrophe at the end of default Regular Expression then click OK.

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To enable new settings save the configuration to the device.

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The suggestion to avoid these problems is denying apostrophe use wherever possible in email addresses.

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