Intermittent SSL errors in branded links

Hey everyone! I’ve got a question regarding link branding & SSL in some of the emails we’ve been sending.

We use Courier to send most of our emails, including invitations to subscribe to our service. In these emails, we pass an SSL secured unique (and rather long) URL that allows users to auth into our site and manage their settings.

Over the past month or two, we’ve received intermittent reports of the SSL handshake failing when users follow the URL to manage their subscriptions. Its a fairly standard (and unfortunately ambiguous) ERR_SSL_PROTOCOL_ERROR, and it appears to be occurring on ...ct0.app links…which I’m guessing is Courier’s proxy link substitution?

We’re having a tough time reproducing and debugging this, so I was curious if you all had any insight into whats going on here?

We’re seeing this across multiple client email service providers, and at least one of them has a confirmed link branding setup working with SendGrid. There are no consistencies between browser, OS, or ESP

I’m happy to provide any additional details that may be helpful. This is killing our customer confidence, so we’d love to figure this out.

Thanks in advance for your time and effort!

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Hey @matt, this is Tejas from Courier Engineering. We are looking into the issue closely, apologies for the subpar experience. Any chance do you happen to know the emails/ message IDs that have resulted into this? We can try reproducing on our end as well, but if we could localize this to something specific it’d be super helpful. (Feel free to share details via intercom instead of the public forum)

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quick question @matt , could you share approximate date/week around when this started occurring? Also would be helpful to know when was the latest occurrence.

Thanks Tejas! I’ll follow up in Intercom with specifics.

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