Now, tentatively, the HSE has said that it is now looking to connect it again with external email later today (17 May).
The HSE network will remain isolated for a further 48 hours to maintain protection from the attack.
Communications Minister Denis Naughten said the global cyber attack was unprecedented.
"We have been lucky in that we have been upgrading our computers and hardware, particularly in the last few years".
Two cyber security firms have suggested a North Korea-linked organisation is behind the attack that's crippled compuer systems around the world.
Symantec and Kaspersky Lab have said some code in an earlier version of the "WannaCry" virus had also appeared in programs used by the Lazarus Group, which researchers from many companies have identified as a North Korea-run hacking operation.
The PSNI has warned workers across Northern Ireland that their systems may already be infeicted by a computer virus and to be on the alert as they return to work on Monday.
The same virus may have infiltrated systems in NI, but not yet been activated, said the PSNI.
The virus, which took control of users' files, spread to 100 countries, including Spain, France and Russian Federation.
The malware has caused severe disruption to health services, industry, transport, academia and law enforcement around the world.
In the Republic, the Health Service Executive (HSE) cut its network off from external communications as a precaution.
This meant that staff were unable to access emails or do any internet related activities over the past few days, but as of yesterday's update staff were able to internally email one another.
The PSNI said its cyber crime centre would continue to actively participate "in the national co-ordinated response to this attack and we would encourage all local businesses and public services to take immediate steps to protect their systems and reduce their vulnerability". It is of the utmost importance that individuals and organisations act to ensure the integrity of our local cyber networks and take appropriate action to reduce the threat posed by cyber criminals. Internal emails had also been blocked, but were restored yesterday morning, and Mr Corbridge said it was unlikely that any of these interruptions would have a significant impact on patient care.