Emails being sent to and from accounts using Spark's email service provider Xtra Mail are still being blocked with small organisations facing financial loss.
More than 50 people have contacted the Herald about issues dealing with Xtra Mail email accounts following an article published in September.
• READ MORE: Issues with Spark email Xtra hitting Kiwi businesses
This is not the first time Spark's platform has been criticised, with customers in the past complaining of receiving large quantities of spam emails.
To combat the issue Spark added an additional spam filter to its system which had since caused restrictions on legitimate emails.
Earlier issues were said to be impacting mostly small business owners or those sending invoices or emails with financial-related wording. The Herald understands the issue has widened and is now also impacting emails of a general nature.
One woman said she had recently stopped receiving emails from genealogy website Ancestry, which she is subscribed to.
"Ancestry has told me the emails are being sent because they can see me in their mailing list," she said.
The woman could not get the issue resolved when she contacted Spark.
"I was given an email address by the first person, to respond [to], she did that because she was transferring me and thought I might get dropped.
"I decided to document my issues and send it to this person. She told me she passed my email and attachment to a team leader but I have had no acknowledgement," she said.
"It's as if it's fallen into a black hole."
The woman's claims of poor support from Spark echo others'.
Hello Club co-founder Adam Reis said his software company first noticed its general emails were bouncing back around a month ago. It was at the beginning of the month when the company sent out its monthly invoices that he realised "something more serious was going on".
Issues with Xtra had hit the business financially and disrupted daily operations.
"Not only do we have to spend extra time working out who we need to re-send invoices to, we have to call up customers to tell them we can't send them any invoices anymore ... it's a lot of time that is going to waste," Reis said.
He said this issue was particularly challenging when it came to customers who opted to communicate exclusively through email.
"There's no other way to reach them or tell them they have an invoice to pay," he said.
Reis called on Spark to do something about it.
"We've called their support team to notify them about this issue but they haven't been very helpful.
"They are pushing us around and saying recipients should add us to their 'safe senders' list but obviously that's not practical if half the country is suddenly no longer able to receive invoices or emails."
Reis did not know how much money Hello Club had lost because of the issue.
"The hassle of having to deal with it and the lost time is the bigger problem for us right now," he said.
"Why doesn't Spark just reverse their last change, fix it and then release it again when it's actually fixed instead of letting this roll on for months."
In a statement to the Herald, Spark spokeswoman Ellie Cross said the nature of the issue meant there was no quick or "permanent fix" to resolve issues with Xtra Mail.
"This is a constant balancing act that all mail service providers have to navigate, stopping "spam email while still allowing for legitimate emails to pass through the system", Cross said.
Why doesn't Spark just reverse their last change, fix it and then release it again when it's actually fixed instead of letting this roll on for months.
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"We're working with our vendor SMX on an ongoing basis to improve the spam filter and ensure legitimate emails are not blocked."
Cross would not comment on the Herald's questions on why Xtra Mail was having issues with its spam blocking filters and other mail service providers were not.
Barry Sanders, IT manager of conservation organisation Forest & Bird, sends out weekly subscription renewal emails to its members but has lost members since Xtra implemented its second spam filter.
"People keep saying 'Oh we've dropped off the membership' and we tell them that's because they haven't paid and they say; 'I never got a renewal' - that's the typical scenario," Sanders said.
"A few weeks ago I went and dived into the back end because it's around the cloud and looked at all of the messages that had gone out, about 33 per cent of the recipients are on Spark or Xtra and there they were as suspected spam."
Sanders said the organisation was now trialling sending membership renewal emails off to Xtra accounts in small batches to see if that makes a difference.
"There are a few words of financial in there and that's what I think the filters are picking up on," he said.
"Why should [their filters] be so much harsher when other carriers aren't."
Spark has 720,000 Xtra Mail customers.