We are trying to send emails via Zoho mail SMTP over SSL, port 465 using PHPMailer (on a Wordpress install). Since Tuesday we've intermittently been having issues with emails sending from our site.  After a lot of debugging we've identified the issue is with the connection itself to Zoho mail, see the log below for an example of the kind of error that comes up:

[17-Jul-2019 14:51:39 UTC] Connection: opening to ssl://smtp.zoho.com:465, timeout=300, options=array (
)
[17-Jul-2019 14:56:39 UTC] Connection: Failed to connect to server. Error number 2. "Error notice: stream_socket_client(): SSL: Handshake timed out
[17-Jul-2019 14:56:39 UTC] Connection: Failed to connect to server. Error number 2. "Error notice: stream_socket_client(): Failed to enable crypto
[17-Jul-2019 14:56:39 UTC] Connection: Failed to connect to server. Error number 2. "Error notice: stream_socket_client(): unable to connect to ssl://smtp.zoho.com:465 (Unknown error)
[17-Jul-2019 14:56:39 UTC] SMTP ERROR: Failed to connect to server: (0)
[17-Jul-2019 14:56:39 UTC] SMTP connect() failed. 

As far as I can tell, this error happens at completely random points as I can't seem to trigger the error with any specific actions. Do you have an ideas what could cause this or what we can do to solve the problem please.   Prior to Tuesday of this week all was fine.